# Presentation: 917661

## Variable Speed Limits

**Variable Speed Limits**

**Making Work Zones Work Better Workshop **
**Orlando, Florida     17 Sept. 03**
- Davey Warren
- Office of Safety  Programs
- Federal Highway  Administration

## Presentation Overview

- What is a variable speed limit?
- How do variable speed limits work?
- Objectives of variable speed limit system
- Work Zone Tests
- Lessons learned
- Future products and additional information

## What is a Variable Speed Limit (VSL)?

- Speed limit changes with changing conditions

**1950**

**Notes:**
Variable speed limits are not new.

Over a half century ago on the Pennsylvania Turnpike, a revised speed limit of 35mi/h was superimposed on the usual 65 to mandate caution in inclement weather.   Source:  Smithsonian Vol. 21 No. 7The Pennsylvania Turnpike: a dream of a road.

Reduced speed limits in school zones during certain times of the day are another form of variable speed limits.  In some cases flashing lights are used to indicate when the lower limit and in other the time is specified on the sign.  A similar type flashing sign has been used in work zones.  

These are what I refer to as poor boy variable speed limits.  
One issue affecting the credibility of these part-time limits is the duration the reduced speed limit is in force.  In some zones the reduced speed is in effect the entire school day.  In others for 45-60 minutes at the beginning and ending of the school day.  Yet most of the activity takes  place with a 15-20 minute window.

## Part-time Speed Limit Work Zone

**Part-time Speed Limit Work Zone**

## Focus of presentation

- Modern systems change the speed limits in real time:
- Traffic conditions
- Adverse weather conditions
- Road surface conditions
- Work Zones

**1960**

**Notes:**
Lodge Freeway
21 speed signs over 3 mi
60-20 mi/h
video surveillance
gradually slow  approaching backups

## Computer controlled limits

## Variable Speed Limit System Components

- traffic and speed detectors
- variable speed signs
- microprocessor
- communication
- environmental sensors
- base station for recording speed limit changes

## Why Use Variable Speed Limits?

**Notes:**
Work zones are dynamic with highly variable speed and road conditions
Safe speed varies with road and traffic conditions
	speed profile from I-40 in Albuquerque
	45 work zone speed limit sign in background not credible
Static speed limits are only good for the condition it was set for
	Too low for normal conditions
	Too high for adverse conditions

## Objectives

- Increase compliance
- Improve safety
- More efficient use of highway
- Less burdened justice system
- Responsive to dynamic conditions
- Provide real time information

## Variable Speed Limit Applications

- General VSL
- Winter Weather and Adverse Road Conditions
- Fog
- Congestion
- Work Zones

## General VSL

- 	Examples
- NJ Turnpike
- I-40 New Mexico
- Germany
- Characteristics
- Typically cover longer stretches of roadway
- Broad range of input criteria for speed limit decision (traffic speed, volume, crashes, congestion, construction, ice, snow, fog, etc.)

## I-40 New Mexico

- fully automated
- maximum speed limit
- constrained by NMSL
- minimum speed limit
- downstream hazard warning
- roadside station after each interchange

## Average Speeds and Variable Limit Over 24 hr

**Average Speeds and Variable Limit Over 24 hr**

## N.M. Automated Speed Control Logic

- Smooth Mean Speed +/-

## Congestion

- Examples
- Lodge Freeway, MI
- M25, UK
- Netherlands
- Characteristics
- Cover stretches of congested roadways
- Speeds set to reflect traffic conditions
- Slow traffic approaching backups

**1960**

**Notes:**
First variable speed system in USLodge Freeway in Detroit Michigan (1960) :
21 speed signs over 3 mi
60-20 mi/h
video surveillance
gradually slow  approaching backups

## Winter Weather and Road Conditions

- Examples
- I-90, Washington
- E18, Finland
- I-40, Arizona
- Characteristics
- Cover longer stretches of weather-susceptible roadways
- Speeds set to reflect roadway/weather/visibility conditions

## Fog

- Examples
- I-75, Tennessee
- I-80, Nevada
- F-6, Australia
- A 16, Netherlands
- Characteristics
- Typically deployed in areas that experience highly variable, severe fog
- Speed and visibility sensors

**Notes:**
Microwave link to police center
Semi-automated

## VSL in Work Zones

- Dynamic conditions in work zones make them excellent candidates for VSL
- FHWA is sponsoring 3 field       tests of VSL in work zones
- Michigan
- Maryland
- Virginia

## VSL in Work Zones

- Examples
- Michigan
- Maryland
- Virginia (on hold)
- Characteristics
- Portable speed trailers
- Typically deployed in longer term work zones

**Notes:**
Dynamic conditions in work zones make them excellent candidates 
FHWA sponsoring three field tests of VSL in work zones
Michigan
Maryland
Virginia (on hold due to Patent Infringement Law suit)

## Field Test Objectives

- Objectives:
- Deploy practical variable speed limit systems in work zones
- Evaluate the effectiveness of the systems on:
- Speed limit compliance
- Credibility of speed limits
- Improved Safety
- Improved Traffic flow

## Michigan’s VSL System

- Four deployments to date
- Where:
- 19-mile work zone
- I-96 near Lansing
- ADT 29k – 53k
- (over 10% trucks)
- When: late May – August 2002
- Duration: Short – All less than 1 week

**Notes:**
ADT= 30-50,000 veh per day
Deployed in one direction only
One was 8- mile section; thin new wearing surface and minor bridge work
	barrel separated workers
	1 of 2 lanes closed
Another 5 mi section was being totally reconstructed-lanes closed on one side and crossed over to other direction
	day and night
	jersey barriers separated traffic
A third section involved concrete patching
	 barrels separated workers
	1-2 of 3 lanes closed at times
Normal speed limit was 70; static work zone speed limit was 50

## I-96 Michigan

- 6-7 variable speed limit trailers
- RTMS Traffic detector
- Solar power
- Controller with RF communication
- LED speed display
- 1⁄2-1 mi spacing
- line of sight communication
- 70 to 40 mi/h
- Based on prevailing speed
- Max based on nature of road work
- Pagers used to transmit speed limit changes to police

**Notes:**
Distributed system
	each trailer can determine speed limt
	each trailer communicates with upstream and downstream trailer
	last trailer serves as master and only one that can be monitored and controlled remotely
	 Vendor- International Road Dynamics (IRD)  Marketed as Speed Ranger
Units basically display prevailing speed of vehicles passing downstream sign (first and last units display prevailing speed at that location)
Speed limits could range from 70 mph to 40 mph (limited for some deployments based on work activities)
Maximum 10 mph speed limit differential between signs
Spaced 0.5-1 mile apart which was closer than desired 1-2.5 mi because curves and overpasses block line of sight for RF communication
Had to put numbers on the back of VSL signs so police would know which speed limit applied to which trailer.
Recommend trailers be numbered and deployed in order that motorists see them

## Michigan’s Speed Control Logic

| Profile | 1   Workers Unprotected | 2 Workers Present | 3 No Work Activity |
| --- | --- | --- | --- |
| L.O. Threshold - 0% | 50 | 60 | 70 |
| H.O. Threshold – 70% | 40 | 40 | 40 |
|         v < 40 | 40 | 40 | 40 |
| 40 ≤ v < 43 | 45 | 45 | 45 |
| 43 ≤ v < 48 | 50 | 50 | 50 |
| 48 ≤ v < 53 | 50 | 55 | 55 |
| 53 ≤ v < 58 | 50 | 60 | 60 |
| 58 ≤ v < 63 | 50 | 60 | 65 |
| 63 ≤ v < 68 | 50 | 60 | 70 |
|         v ≥ 68 | 50 | 60 | 70 |

**Notes:**
Units basically display prevailing speed of vehicles passing downstream sign
   (first and last units display prevailing speed at that location)
Average speed updated every 6 min; user selectable between 5 and 15.
Speed limits could range from 70 mph to 40 mph (limited for some deployments based on work activities)
Each trailer could have a different profile depending on nature of road work activity
Maximum 10 mph speed limit differential between signs

## Michigan’s VSL System

- Preliminary Results:
- Better compliance
- More uniform speeds during off-peak
- Travel times reduced
- Greater speed reduction at crossover
- RTMS accurate for volume but marginal for speed
- Trailers can be set-up within 10 minutes

**Notes:**
Rapidly changing work zone made evaluation difficult
Only preliminary results are available
Displayed speed and operating speeds generally increased
Average speed generally below displayed speed for VSL but not static 50
More consistent speeds during non-peak periods, especially at night
RTMS radar generally 2-4 mi/h below speed monitoring equipment using road tubes 

## Maryland’s Work Zone VSL

- VSL Trailers – 4
- Radar unit for speed
- Queue Detector Trailers – 2
- Variable Message Signs on Trailers – 2
- Base Unit – Central Control (CHIPS System Trailer) – 1

**Notes:**
Sign mimics standard speed limit sign—super bright WHITE LED’s
Based on user specified percentile speed based on work activity
Example: if work is taking place between 8:30 and 3:30, post at 50 percentile speed; when not working post at 70 percentile speed 
Speed limit based on 5-10 minute samples updated no more frequently than every 2 minutes.
Maryland team also has 2 other candidate algorithms programmed- Tweener & Oz

## Maryland’s VSL Algorithms

- Logic:
- User selectable percentile speed
- Percentile can vary depending on whether workers present or not
- User can specify times to switch percentile
- Speed limit will be updated no more frequently than every 2 minutes.
- 2 other candidate algorithms programmed
- Tweener
- Oz

**Notes:**
Tweener incorporates information from the downstream speed trailer in the logic.
Oz is intended to maximize headways and harmonize speeds  during onset of congestion

## Maryland’s VSL System Status

- Status:
- Completed pre-deployment testing and accepted equipment
- First deployment will occur in the next month
- The second deployment has yet to be scheduled

## Lessons Learned

- Engineering
- Perform “off-site” testing on a real road
- Eliminate unnecessary fluctuations in limit
- May need to change as often as once a minute
- Need signs on both sides of road with 3 or more lanes
- Implementation
- Make sure that all stakeholders are on board and working towards common goals
- Don’t try to do everything all at once – start with something easy
- Work closely with the media; have only 1 or 2 PR people for the media to contact
- Be flexible (expect the unexpected)

## Summary

- VSL being used around the world to help manage speed and improve safety
- VSL seems to be particularly appropriate for work zones
- Enforcement remains an issue
- More and better data needed on effectiveness

## Additional Information

- http://www.itsdocs.fhwa.dot.gov/itsweb/welcome.htm
- Examples of Variable Speed Limit Applications (EDL#12164)
- Safety Applications of ITS in Rural Areas (EDL#13609 )
- http://gulliver.trb.org/publications/nchrp/nchrp_lrd_47.pdf
- NCHRP Legal Research Digest 47: Judicial Enforcement of Variable Speed
- http://safety.fhwa.dot.gov/fourthlevel/pdf/poynton1.pdf
- Controlled Motorways: Variable Speed Limits on the M-25, UK
- http://safety.fhwa.dot.gov/fourthlevel/ppt/Warren_Vsl.ppt
- Variable Speed Limit slide show
- Future Products
- NCHRP 3-59 Variable Speed Limit Implementation Issues (2004)
- Field Test Evaluation Cross-Cutting Study Report (2004)

**Notes:**
NCHRP Project is focusing on enforcement issues.  Will be testing Technology Assisted Speed Enforcement in work zone in conjunction with Penn Turnpike Authority
	Photo radar image to be transmitted to police vehicle station downstream who would then apprehend offender and issue citation.

In addition to cross-cutting report in 2004, will delivier two brochures:
One for decision makers:  “Why should I use VSL in Work Zones?”
One for engineers: “How do I include VSL in Work Zones?”

## Questions

- Davey Warren
- FHWA HSA-20
- 400 7th Street, SW
- Washington, DC 20590
-  202-366-4668

**davey.warren@fhwa.dot.gov**