Wyoming Administrative Code › Agency 045 - Transportation, Dept. of › Sub-Agency 0003 - General Agency, Board or Commission Rules › Chapter 30 - PROCEDURES FOR LOCALLY ESTABLISHING SPEED LIMITS › Appendix II - Standards and Procedures for Establishing Speed Limits on Wyoming Unpaved Roads › Section 1.2 - DATA COLLECTION/ANALYSIS

Current through July 13, 2024
(1)
All of the spot speed
					 data and other information described in this section shall be collected by
					 engineers or technicians who have been properly trained by the Wyoming
					 T2/LTAP Center to collect field data.
(2)
The data analysis
					 required to make the final recommendations on setting proper speed limits can
					 be conducted by professional engineers only. Those professional engineers are
					 not required to visit the actual location where the study is being conducted as
					 long as the required data was collected by trained technicians or
					 engineers.
(3)
For the engineering
					 studies, vehicle speeds and traffic volumes should be determined using
					 automated traffic counters. Each automated traffic counter should consist of a
					 traffic counter device, two pneumatic tubes, and some additional accessories.
					 The two pneumatic tubes are placed across the road at the recommended spacing.
					 Two ends of the tubes are fixed on the shoulder, while the other two ends are
					 connected to the traffic counter device.
(4)
For most low volume
					 unpaved roads, 7 consecutive days of traffic counts are required. For unpaved
					 roads with more than 200 vehicles per day, 2 days of traffic counts may be
					 adequate. Selecting the spot to take speed measurements-the location, traffic,
					 and weather conditions under which to conduct the spot speed study-is generally
					 a matter of common sense. Since average speeds over the length of a section of
					 roadway are the main interest, speed measurements should be taken at the
					 midpoint of a typical section.
The most important aspect of the location is to avoid areas
					 of acceleration and deceleration, such as access points, curves, bad drainage
					 areas, and locations close to roadside hazards. The final layout of the data
					 collection site should be fully described in any report of speed data. The crew
					 should make an accurate sketch of the site, showing the roadway widths and the
					 position of the traffic counters. The crew should record the start time, end
					 time, any downtime, and the conditions prevailing during the study. Such
					 conditions should include a description of any significant road surface
					 distresses. It is essential that speed studies are performed only on roadway
					 segments with average surface conditions.
(5)
A special form was
					 developed to assist with the collection and analysis of the traffic count data
					 and the safety aspects of the road as shown in Figure 1-1. The form includes
					 five parts: general information, automated traffic count values, roadway
					 characteristics, historical crash data, and range of speed limit values. In the
					 form, the clear boxes correspond to input that trained technicians or engineers
					 are required to obtain. The gray shaded boxes correspond to the calculations
					 and information that the professional engineer is required to provide. An
					 example of a completed unpaved roads speed limit form is shown in Figure
					 1-2.
(6)
When collecting speed
					 study data, the general information should be completed before proceeding to
					 the next steps.
(7)
The required automated
					 traffic count values can be obtained from the output file that the automated
					 traffic counters produce. As shown in Figure 1-3, the output file summarizes
					 the different speed and traffic volumes that the automated traffic counters
					 produce. Four of these values are required in the form and they are:
					 85th percentile, 50th
					 percentile, the Average Daily Traffic (ADT) and the Average Daily Truck Traffic
					 (ADTT).
Figure 1-1 Unpaved Roads Speed Limit
					 Form
GENERAL INFORMATION
LOCAL JURISDICTION:
ROUTE:
LOCATION:
DATE:
AUTOMATED TRAFFIC COUNT VALUES
85th PERCENTILE:
50th PERCENTILE:
UPPER BOUND OF THE PACE SPEED:
AVERAGE DAILY TRAFFIC:
AVERAGE DAILY TRUCK TRAFFIC:
ROADWAY CHARACTERISTICS
ROADWAY LENGTH:
NUMBER OF ACCESS POINTS:
ACCESS POINTS PER MILE:
ROADWAY WIDTH:
ADJACENT LAND-USE:
TYPE OF TERRAIN:
HISTORICAL CRASH DATA
FATAL:
INJURY:
PDO:
EPDO:
EPDO PER MILE:
RANGE OF SPEED LIMIT (MAXIMUM = 55
								MPH)
PREFERRED SPEED LIMIT:
LOWEST ACCEPTABLE SPEED LIMIT:
Figure 1-2 Example of a Completed Unpaved Road Speed
					 Limit Form
GENERAL INFORMATION
LOCAL JURISDICTION:
Smart County
ROUTE:
700
LOCATION:
MP 16.1 to MP 26.1
DATE:
7/1/2011
AUTOMATED TRAFFIC COUNT VALUES
85th PERCENTILE:
43.9
50th PERCENTILE:
35.7
UPPER BOUND OF THE PACE SPEED:
40.4
AVERAGE DAILY TRAFFIC:
141
AVERAGE DAILY TRUCK TRAFFIC:
4
ROADWAY CHARACTERISTICS
ROADWAY LENGTH:
10
NUMBER OF ACCESS POINTS:
63
ACCESS POINTS PER MILE:
63 / 10 = 6.3
ROADWAY WIDTH:
20
ADJACENT LAND-USE:
Recreation/Scenic
TYPE OF TERRAIN:
Rolling
HISTORICAL CRASH DATA
FATAL:
0
INJURY:
5
PDO:
8
EPDO:
9.5*0 + 3.5*5 + 8 = 25.5
EPDO PER MILE:
25.5 / 10 = 2.55
RANGE OF SPEED LIMIT (MAXIMUM = 55
								MPH)
PREFERRED SPEED LIMIT:
43.9 rounded to nearest 5 = 45
LOWEST ACCEPTABLE SPEED LIMIT:
45 - 10 = 35
Click to
					 View Image
(8)
Roadway characteristics
					 should be collected during the field inspection of the road The list and
					 description of each characteristic that are included in the form are as
					 follows:
Roadway Length: The length of the road in miles.
Access Points: Total number of access points on the whole
					 roadway length.
Access Points per Mile: Divide the number of access points
					 by the roadway length.
Roadway Width: The total width of the road including both
					 shoulders.
Adjacent Land-Use: Refers to the type of users of the road.
					 The following different types of land-uses were obtained from AASHTO's
					 Guidelines on Geometric Design for Very Low Volume Roads:
.
Rural major access roads
serve
					 a dual function of providing access to abutting properties as well as providing
					 through or connecting service between other local road or higher type
					 facilities.
.
Rural minor access roads
serve
					 almost exclusively to provide access to adjacent property. The length of minor
					 access roads is typically short. Because their sole function is to provide
					 access, such roads are used predominantly by familiar drivers.
.
Industrial or commercial access
					 roads
serve developments that may generate a significant proportion of
					 truck or other heavy vehicle traffic. These roads are classified separately
					 from minor access roads, which they otherwise resemble, because of the
					 consideration for trucks and other heavy vehicles.
.
Recreation and scenic roads
serve specialized land uses, including parks, tourist attractions, and
					 recreation facilities, such as campsites or boat-launch ramps. Their users are
					 often unfamiliar drivers and serve recreational vehicles including motor homes,
					 campers, and passenger vehicles pulling boats and other trailers.
.
Rural resource recovery roads
are local roads serving logging or mining operations. Resource recovery roads
					 are distinctly different from the other functional subclasses of very
					 low-volume local roads in that they are used primarily by vehicles involved
					 with the resource recovery activities and the driving population consists
					 primarily or exclusively of professional drivers with large vehicles.
.
Rural agriculture roads
are
					 used primarily to provide access to fields and farming operations. Vehicle
					 types that use such roads include combines, tractors, trucks that haul
					 agricultural products, and other large and slow-moving vehicles with unique
					 operating characteristics.
Type of Terrain: Refers to the general geometrics of the
					 road. There are three different types of terrain that can be chosen:
.
Level
.
Rolling
.
Mountainous
(9)
The historical crash data
					 can be obtained from the safety division of WYDOT or the Wyoming T2/LTAP Center
					 to get the latest crash statistics. It is recommended that 10 years of crash
					 data be included in the evaluation The following three types of crashes are
					 required: number of fatalities, number of injuries, and the number of Property
					 Damage Only (PDO). The Equivalent Property Damage Only (EPDO) is calculated by
					 Equation 1.
EPDO = 9.5 * Fatalities + 3.5 * Injuries +
					 PDO
(Equation 1)
Once the EPDO is calculated, the EPDO per mile is
					 determined by dividing the EPDO by the roadway length.
(10)
The preferred speed
					 limit is the 85th percentile speed rounded to the
					 nearest 5 mph. The lowest acceptable speed limit may be up to 10 mph less than
					 the preferred speed limit.