Innovative Traffic Control Devices for Improving Safety at Rural
Short-Term Maintenance Work Zones

# Michael D. Fontaine

# Texas Transportation Institute

Texas A&M University System

3135 TAMU

# College Station, TX 77843-3135

Phone: (979) 845-9929

E-mail: m-fontaine@tamu.edu

The Texas Department of Transportation (TxDOT) maintains almost 80,000
miles of roadway, and rural roads with an average daily traffic (ADT) of
less than 2000 vehicles per day represent more than half of all
lane-miles. As the state's highway system continues to age, drivers are
encountering maintenance activities on these low-volume rural facilities
with increasing frequency. The Texas *Manual on Uniform Traffic Control
Devices* establishes standard practices for installing work zone traffic
control when maintenance work is performed (*1*). Although the *MUTCD*
provides basic guidance for installing work zone traffic control, there
is the potential to improve safety by utilizing innovative
countermeasures.

Much of the maintenance work performed on low-volume rural roads is
completed in a single day. The short duration of these work zones can
create a number of safety challenges. First, it is often difficult to
coordinate work zone speed enforcement for these sites with local law
enforcement agencies. Many rural enforcement agencies have limited
resources, and it can be difficult to schedule enforcement activities
when the location of work zones change daily. In Texas, most rural roads
have a posted regulatory speed limit of 70 mph, but regulatory speeds
are usually not reduced for short-term work zone activities. Traffic
control is often limited to devices that can be easily installed and
removed by a work crew due to the short duration of maintenance
activities.

#### PROJECT OBJECTIVES

TxDOT and the Federal Highway Administration (FHWA) sponsored a Texas
Transportation Institute (TTI) research project to determine if
innovative traffic control devices could improve safety at short-term
rural maintenance work zones. This project examined several innovative
countermeasures to determine if they would produce a positive safety
benefit at short-term rural work zones. The following objectives were
established to evaluate the devices:

-   identify devices not currently used by TxDOT that could potentially
    improve safety at temporary traffic control zones by either reducing
    speeds, improving worker visibility, or increasing awareness of the
    upcoming work zone;

-   determine the impact of the devices by conducting field evaluations;
    and

-   assess the feasibility of using these devices at short-term
    maintenance sites.

With these goals in mind, five different traffic control devices were
selected for further evaluation:

-   speed display trailers,

-   radar drones,

-   portable rumble strips,

-   alternative worker vests, and

-   fluorescent orange roll-up signs.

This paper describes the results of the evaluation of these devices.
Recommendations for the application of these devices to short-term work
zones are also made.

**DESCRIPTION OF COUNTERMEASURES**

![](media/image1.wmf){width="3.001388888888889in" height="2.6in"}**Speed
Display Trailer**

Speed display trailers detect the speed of approaching vehicles using a
radar unit. These speeds are then displayed to oncoming drivers using
large numerals on the face of the display. Figure 1 shows the speed
display trailer used in this study. The display tested in this
evaluation used Ka band radar and displayed speeds in 24-inch high light
emitting diode (LED) numerals. The display also had a speed-activated
strobe light that flashed when vehicles were detected traveling over a
preset speed threshold. Throughout this study, the strobe light was
activated when a vehicle was detected traveling more than 5 mph over the
speed limit.

**Radar Drone**

![](media/image2.png){width="3.5in" height="1.617361111111111in"}Radar
drones simulate the presence of law enforcement by continuously emitting
radar signals. Vehicles with radar detectors may decelerate when they
detect the radar transmission, thinking that an officer is performing
speed enforcement ahead. Figure 2 shows the radar drone evaluated in
this study. The radar drone used in this evaluation emitted a K band
radar signal that could be detected up to a mile away.

**Portable Rumble Strips**

Rumble strips can be used to provide an auditory and vibratory cue to
drivers that they are about to enter a work zone. The portable rumble
strips used in this study were 12 feet long, 4 inches wide, and 0.25
inches thick. The rumbles strips were installed by removing the
protective backing, placing the rumble strip on the road surface, and
using a weighted roller to firmly adhere the strip to the pavement. Each
rumble strip installation consisted of a series of six rumble strips
placed parallel to one another at 18-inch spacings. Figure 3 shows a
typical portable rumble strip installation.

![](media/image3.png){width="3.290277777777778in"
height="2.1131944444444444in"}

**Alternative Worker Vests**

At the time of this study, TxDOT workers wore fluorescent orange mesh
vests. There was some concern that the color of these vests may cause
workers to be camouflaged by work zone traffic control devices.
Fluorescent yellow-green worker vests offered the potential to better
distinguish workers from surrounding traffic control than the standard
TxDOT orange vest. This evaluation examined five different worker
garments in order to determine if worker conspicuity could be improved.
These garments are shown in Figure 4. The garments were evaluated based
on both their visual performance and the wearer's comfort level. The
vests in Figure 4, from left to right, are:

-   TxDOT orange mesh vest,

-   Proposed TxDOT yellow-green mesh vest,

-   Mesh yellow-green vest,

-   Solid fabric yellow-green vest, and

-   Yellow-green jacket with sleeves.

It should be noted that American National Standards Institute (ANSI)
standard ANSI/ISEA 107-1999 was released after this evaluation was
performed (*2*). The proposed TxDOT yellow-green vest did not meet the
requirements for background material for small and medium vests.

![](media/image4.wmf){width="5.904861111111111in"
height="1.4666666666666666in"}

![](media/image5.wmf){width="1.7597222222222222in"
height="1.4423611111111112in"}**Fluorescent Orange Roll-Up Signs**

Fluorescent orange roll up signs were also evaluated during this study.
It was hypothesized that these signs would improve driver awareness of
the approaching work zone by increasing the conspicuity of the signs.
These signs could be implemented at a site without placing any
additional burden on the maintenance workers at the site. The size of
the signs evaluated was 48 inches by 48 inches.

**METHODOLOGY**

Most traffic control devices were examined primarily through field
tests. The effect of a countermeasure was examined by comparing several
measures of effectiveness with and without the device present. Some
limited closed-course testing was also performed to evaluate the
alternative worker vests.

**Field Data Collection**

Field testing occurred in north Texas near Oklahoma. All test sites had
70 mph posted regulatory speed limits and level grades. A mix of four
lane and two lane sites were evaluated, and the length of the activity
area at these sites was typically between ¼ and ½ mile. In all cases,
the work sites were only in place during daylight hours for a single
day. Table 1 summarizes the sites used to evaluate each device.

#### Table 1. Data Collection Site Summary.

  ---------------------------- ------------------ -----------------------
  **Device Evaluated**         **Number of        **ADT (vpd)**
                               Sites**            

  Speed display trailer        4                  1000-8900

  Radar drone                  3                  6900-8900

  Portable rumble strips       3                  1250-1850

  Alternative worker vests     6                  410-8900

  Fluorescent orange roll-up   7                  410-8900
  signs                                           
  ---------------------------- ------------------ -----------------------

Since each site was only in place for a single day, all testing at a
location had to be completed in one day. Data were collected in two
phases at each site. First, data were collected with only the work zone
traffic control required by the *MUTCD* present. Approximately halfway
through the day, the test treatment was installed in addition to the
*MUTCD-*required traffic control. Table 2 summarizes the measures of
effectiveness (MOEs) that were established for each device.

**Table 2. Measures of Effectiveness for Each Device.**

  ------------------------ -------------- --------------- ------------ ------------
  **Device**               **Traffic      **Conflicts**   **Worker     **Driver
                           Speed**                        Comments**   Comments**

  Speed display trailer                                             

  Radar drone                                                       

  Portable rumble strips                                            

  Alternative worker vests                                            

  Fluorescent orange                                                  
  roll-up signs                                                        
  ------------------------ -------------- --------------- ------------ ------------

Traffic speed was measured using lidar guns and traffic counters. This
MOE was used to determine if the countermeasure reduced speeds on the
approaches to the temporary traffic control area and within the work
zone activity area. Since the work zone was only in place for a short
time, conflicts were used as a surrogate measure for safety. The
approach to the work zone activity area was videotaped in order to
examine conflicts between vehicles, such as late merges, sudden braking
maneuvers, or other actions that caused surrounding vehicles to brake or
perform evasive action. The workers at the job site were also
interviewed in order to assess the potential usability of the devices
for short-term operations. Finally, drivers were interviewed at some
low-volume sites to determine their opinions on the measures being
evaluated.

#### Closed Course Evaluation

Closed course evaluations were also conducted to assess the luminance
and contrast ratio of the alternative worker vests. All measurements
were made under ambient daylight illumination between 11:00 AM and 4:00
PM on a clear day in August. Since this project focused on daytime
operations, the retroreflectivity of the vests was not evaluated.

Luminance can be thought of as the brightness of the vest, while
contrast ratio measures how much a vest stands out from a background.
This was done in order to obtain objective performance data for the
various vests. The luminance of the vests was determined by measuring a
worker wearing a vest in front of a simulated work zone. The worker wore
the vest over a dark t-shirt, and was stationed in the same position as
a flagger at the beginning of the work zone. The luminance of the vest
was then measured from approximately 500 feet away using a
telephotometer. This was repeated for each of the five worker garments
evaluated.

A second series of measurements were collected in order to determine the
luminance contrast ratio of the vests against a variety of backgrounds.
The contrast ratio is defined as the ratio of the vest luminance to the
luminance of the background. The larger the ratio, the more the vest
"stands out" from the background. The measurements of the vest were made
against the following backgrounds:

-   open concrete road,

-   open asphalt road,

-   mix of fluorescent and standard work zone traffic control,

-   white pickup truck (typical of TxDOT vehicles),

-   foliage typical of a Texas summer, and

-   a yellow construction front end loader.

#### EVALUATION RESULTS

This section summarizes the results of the evaluations of each of the
five devices. A brief description of each countermeasure is provided,
followed by a summary of the results of the evaluation.

#### Speed Display Trailers

The speed display trailer was field tested at four sites. Two of these
sites were at lane closures on a four-lane divided highway, while the
remaining two occurred on two-lane roads where traffic was being
diverted onto the shoulder. Traffic speed, conflicts, and worker
comments were used to assess this device.

Table 3 summarizes the average speed results obtained when the speed
trailer at the four test sites. In general, the speed trailer was
effective in reducing vehicle speeds at all sites. Mean speeds were
reduced by an average of 5.2 mph within the advance warning area for
both cars and large trucks. Speed reductions were slightly less within
the activity area of the work zone.

Table 3. Average Speed Results for Speed Display Trailer.

  ----------- --------------- --------------- --------------- ---------------
  **Vehicle   **Change in                     **Change in %   
  Type**      Mean Speeds**                   Exceeding Speed 
                                              Limit**         

              **Before        **Activity      **Before        **Activity
              Taper**         Area**          Taper**         Area**

  Cars        -5.2            -3.9            -6.9%           -4.4%

  Trucks      -5.2            -2.4            -15.7%          -11.6%
  ----------- --------------- --------------- --------------- ---------------

The video data were examined in order to determine if the speed display
influenced conflicts or aggressive behavior approaching the taper. The
video data showed a slight decrease in conflict rate at one site, but no
discernable impact was observed at the remaining sites.

Worker comments on the speed display trailer were almost uniformly
positive. Workers felt that it was quick and easy to set up. Researchers
noted that the trailer could be installed and removed within 10 minutes.
The maintenance crews felt that the trailer increased awareness of the
work zone and significantly lowered speeds in the activity area.

#### 

#### Radar Drones

The radar drone was tested at three sites. The radar drone was placed in
a vehicle stationed at the start of the advance warning area at all
sites. Speed data were collected approximately 1000 feet before the
start of the taper and approximately halfway through the work zone
activity area.

Table 4 summarizes the speed results for the radar drone. The radar
drone did not significantly impact the speeds of vehicles traveling
through the work zone. The average speed reductions observed were no
greater than 1.6 mph, and only small changes in the number of vehicles
exceeding the speed limit were observed.

Table 4. Average Speed Results for Radar Drone.

  ----------- --------------- --------------- --------------- ---------------
  **Vehicle   **Change in                     **Change in %   
  Type**      Mean Speeds**                   Exceeding Speed 
                                              Limit**         

              **Before        **Activity      **Before        **Activity
              Taper**         Area**          Taper**         Area**

  Cars        +0.5            -0.3            +10.0%          -2.3%

  Trucks      -1.6            -0.5            -7.1%           -2.1%
  ----------- --------------- --------------- --------------- ---------------

Since only a subset of the traffic stream possesses radar detectors,
there were no observable widespread trends in driver behavior. Worker
reaction to the radar drone was mixed. While they felt that the drone
was quick and easy to set up, they were unsure if it would remain
effective if used for extended periods.

#### 

#### Portable Rumble Strips

The portable rumble strips were tested at three sites. Two separate
rumble strip installations were installed at the sites. Each
installation consisted of six individual rumble strips placed
perpendicular to the direction of traffic across the road. The
installations were placed approximately 500 feet and 1000 feet from the
start of the taper.

Table 5 shows the speed results that were collected with the rumble
strips. Passenger cars generally experienced smaller changes in speed
than large trucks did. It is possible that the larger viewing angle of
truck drivers made the rumble strips more visible, and therefore they
responded by decelerating more than cars did.

Table 5. Average Speed Results for Portable Rumble Strips.

  ----------- --------------- --------------- --------------- ---------------
  **Vehicle   **Change in                     **Change in %   
  Type**      Mean Speeds**                   Exceeding Speed 
                                              Limit**         

              **Before        **Activity      **Before        **Activity
              Taper**         Area**          Taper**         Area**

  Cars        -1.6            +0.7            -2.8            -2.5

  Trucks      -4.0            -3.5            -1.6            +0.2
  ----------- --------------- --------------- --------------- ---------------

#####  

Very few erratic maneuvers were observed when the portable rumble strips
were used. Two cars were observed to cross into the opposing lane in
order to go around the rumble strips. All of these maneuvers occurred in
a passing zone when there was no oncoming traffic.

The maintenance crews were very concerned with the installation time
required for the portable rumble strips. It took 40 minutes for a crew
of three people to install all of the rumble strips on a low volume
road. The removal of rumble strips was accomplished in less than 10
minutes. The maintenance crews commented that the installation time for
the rumble strips would take away from the time available to perform
actual work activities. There was also concern that it would be
difficult to install the rumble strips on four-lane roads or under high
traffic volumes without completely stopping oncoming traffic. Although
the workers felt that installation time was too lengthy, they did feel
that the portable rumble strips might produce some benefit in safety.
They felt that the rumble strips would improve driver awareness of the
upcoming work zone and also create speed reductions.

#### 

#### Alternative Worker Vests

##### 

##### Field Evaluation

The worker vests were evaluated at 6 field sites. The solid fabric
worker vests were used during this testing since they provided the
maximum amount of fluorescent fabric and retroreflective material.
Workers were asked to wear the vest for an afternoon, and then comment
on their perceptions of its comfort and visibility. Worker comments on
the vests were positive. They felt that the vests were more visible than
the orange vests. They also felt that the garments were comfortable, and
that the solid fabric vest was not noticeably warmer than the standard
TxDOT mesh vest.

A downstream driver survey was also conducted at two sites in order to
determine if drivers noticed the new worker vest more than the normal
TxDOT worker vest. Approximately 4 percent of drivers noticed that the
workers were wearing yellow vests rather than orange vests.

##### 

##### Photometric Testing

The field luminance of the five worker garments was measured to assess
how bright each garment appears to the eye. The field luminance factor
should be between 0 and 100, with low numbers representing dark colors
and high numbers representing very bright colors. Table 6 summarizes the
field luminance factors determined for the five garments. The
fluorescent yellow green solid vest had the largest field luminance of
all garments tested.

Table 6. Results of Luminance Testing for Vests.

+---------------------------------------+---------------+--------------+
| ###### Garment                        | **Field       | **Field      |
|                                       | Luminance     | Luminance    |
|                                       | (cd/m^2^)**   | Factor (%)** |
+---------------------------------------+---------------+--------------+
| TxDOT Fluorescent Orange Mesh Vest    | 3570          | 35.5         |
+---------------------------------------+---------------+--------------+
| TxDOT Fluorescent Yellow-Green Mesh   | 5926          | 58.9         |
| Vest                                  |               |              |
+---------------------------------------+---------------+--------------+
| Alternative Fluorescent Yellow-Green  | 3431          | 34.1         |
| Mesh Vest                             |               |              |
+---------------------------------------+---------------+--------------+
| Fluorescent Yellow-Green Solid Vest   | 7998          | 78.4         |
+---------------------------------------+---------------+--------------+
| Fluorescent Yellow-Green Solid Jacket | 7197          | 71.5         |
+---------------------------------------+---------------+--------------+

The luminance contrast ratio was also determined for each worker
garment. The larger the contrast ratio, the more the vest "stood out"
from the surrounding background. Thus, larger ratios tend to indicate
that the vest is more conspicuous. Table 7 shows the luminance contrast
values determined for the various vests. The fluorescent yellow-green
solid vest produced the highest contrast ratios for 6 of the 8
backgrounds evaluated. The fluorescent yellow-green solid jacket
performed the best for the remaining two alternatives, but the jacket is
probably not a feasible alternative for workers to wear during the Texas
summer. If a mesh vest is needed to accommodate workers during summer
heat, the proposed TxDOT fluorescent yellow-green mesh vest appears to
be the best alternative

#### Table 7. Worker Vest Luminance Contrast Ratios.

  -------------------- ---------------- --------- ------------- -------------- ------------- -------- --------- ----------
  **Garment**          **Background**                                                                           

                       **Lane Closure** **Sky**   **Asphalt**   **Concrete**   **Foliage**   **Work   **White   **Yellow
                                                                                             Zone**   Truck**   Loader**

  TxDOT Fl. Orange     2.00             0.88      1.54          0.90           1.99          1.14     0.67      2.24
  Mesh Vest                                                                                                     

  Proposed TxDOT Fl.   3.21             1.42      2.33          1.68           3.56          1.61     0.28      3.64
  Yellow-Green Mesh                                                                                             
  Vest                                                                                                          

  Alternative Fl.      1.89             0.83      1.32          0.84           2.16          1.19     0.71      1.94
  Yellow-Green Mesh                                                                                             
  Vest                                                                                                          

  Fl. Yellow-Green     4.30             1.90      3.06          2.46           4.76          2.19     1.51      4.75
  Solid Vest                                                                                                    

  Fl. Yellow-Green     4.61             2.04      2.64          1.97           4.07          1.97     1.41      4.70
  Solid Jacket                                                                                                  
  -------------------- ---------------- --------- ------------- -------------- ------------- -------- --------- ----------

**Fluorescent Orange Roll-Up Signs**

The primary MOEs for the fluorescent orange roll-up signs were worker
comments and driver comments. Traffic data were collected in order to
examine the speeds of the traffic stream, but the signs did not produce
any significant impact on measurable traffic variables.

Maintenance crew comments on the fluorescent orange signs were positive.
They felt that the signs were more visible than conventional roll-up
signs. The workers were also pleased that the set up and removal of this
treatment would not take any more time than they already spend
installing signs.

The fluorescent orange signs were perceived positively by motorists.
Approximately 15 percent of drivers surveyed noted that the signs
appeared brighter than normal when asked if they noticed anything
different about the work zone. The drivers that noticed the signs stated
that they felt that the signs made them more aware of work zone
conditions.

#### SUMMARY OF RESULTS

This section provides a brief assessment of each countermeasure's
applicability to short-term rural maintenance work zones.

#### Speed Display Trailer

-   The speed display trailer produced the largest speed reductions of
    all the devices tested. Average speed reductions of approximately 5
    mph were achieved.

-   Workers felt that the speed display trailer was appropriate for use
    at short-term rural work zones. They felt that the trailer produced
    significant speed reductions and the installation and removal of the
    trailer was reasonable for a short-term work zone.

#### Radar Drone

-   The radar drone produced smaller speed reductions than the speed
    display trailer, averaging less than 1 mph. The effectiveness of
    this device is dependent on the number of vehicles with radar
    detectors in the traffic stream.

-   Workers felt that the drone was very easy to set up and remove, but
    questioned its effectiveness when applied for long periods.

#### Portable Rumble Strips

-   Speed reductions for the rumble strips were between 1.5 and 4 mph.

-   Installation of the rumble strips took a three-person crew 40
    minutes under light traffic. Maintenance crews were concerned that
    the amount of time required to install the portable rumble strips
    would be excessive for many short-term work zones. The rumble strips
    may be better suited to longer-term applications.

#### Worker Vests

-   Fluorescent yellow-green worker vests tended to possess a higher
    luminance and contrast ratio than traditional orange worker vests.
    The fluorescent yellow-green solid vest generally performed the best
    out of the alternatives examined. The proposed TxDOT yellow-green
    worker vest performed the best of all mesh vests tested.

-   Workers believed that the yellow-green vests were more visible than
    the orange vests, and felt that the solid weave vests were not
    significantly warmer than the mesh vests.

#### Fluorescent Orange Signs

-   The fluorescent orange signs did not have any measurable impact on
    the speed of traffic in the work zone.

-   Workers felt that the signs offered improved visibility over
    conventional roll-up signs, and also did not think that the signs
    would increase the amount of time required to install or remove
    traffic control at the site.

-   Driver comments about the signs were positive, and many drivers
    commented that the signs appeared brighter than usual.

#### REFERENCES

1.  *Texas Manual on Uniform Traffic Control Devices for Streets and
    Highways, Part VI: Standards and Guides for Street and Highway
    Construction, Maintenance, Utility, and Incident Operations.* Texas
    Department of Transportation, Austin, TX, 1995.

2.  *American National Standard for High-Visibility Apparel.* American
    National Standards Institute, Arlington, Virginia, 1999.