# Presentation: 656499

## SPEED MANAGEMENT WORKSHOPTRB Special Report 254Engineering Issues

- J. W. Hall
- University of New Mexico

## Study Scope

- Speed limit setting practices
- Speed-safety relationships
- Speed limit effectiveness
- Enforcement & compliance
- Emerging technologies
- Benefits and costs
- Highway environment changes

## Study Process

- Diverse panel
- Literature review
- Invited guests
- Sponsors’ representatives
- Commissioned papers
- Vigorous debate

## SR 254’s Audience

- State legislators
- Local officials
- Law enforcement
- Judicial officers
- Traffic engineers
- Interested general public

## Why Regulate Speed?

- Externalities - risks that drivers impose on others
- Drivers’ inability to:
- Judge vehicle capability
- Anticipate roadway conditions
- Misjudgment of speed’s effect on crash severity

## Slide 6

**Notes:**
Field photo of US 550 NB between Silverton and Ouray, CO.  Road is about 22 feet wide, drop-off is extremely sharp and there is no room for guardrail.  Motorists comply with the posted speed limit of 20 mph due to the visual clues they get from the roadway. 

## Types of Speed Limits

- Basic Rule
- Statutory
- Differential
- Variable
- Speed zone
- Absolute
- Prima facie
- Advisory
- Actual practice

## Slide 8

**Notes:**
Set of four slides showing field conditions associated with speed limits.  In most cases, the engineer did a poor job of establishing and/or posting the speed limit.

## Speed and Crash Theory

- Crash severity
- Laws of physics
- Mitigated by vehicle & road design
- Crash probability
- Higher information processing rate
- Traffic conflicts
- Risk-homeostasis

## Speed and Crash Studies

- Speed of crash-involved vehicles is rarely known
- Individual vs. aggregate characteristics
- High speed - high severity
- Safest near the median speed
- Prefer small dispersions
- Numerous contributing factors

## Legislated Speed Limits

- Based on road class
- Seek technical advice
- Relevant factors
- Design speed
- Vehicle operating speed
- Safety experience
- Enforcement experience
- Periodic review

## Speed Zones

- Alter statutory limits based on an engineering study
- 85 percentile speed
- Area type
- Crash experience
- Volume & composition
- Design features
- Pedestrians & bicycles
- Roadway surface
- Nearby speed limits

## Slide 13

## Who asked for this regulation, anyway?

## Motorist Compliance

- What is compliance?
- Who are the *speeders*?
- Effect of altering the speed limit
- Was old limit *reasonable*?
- Is new limit *reasonable*?
- 55 mph NMSL
- Imposed 1974
- Allow 65 mph in April 1987
- Eliminated in 1995

## Slide 16

**Notes:**
Slide of Interstate highway in New Mexico with 55 mph speed limit during the period of the NMSL.

## Garrey & Dewey

- I-25 NB Santa Fe
- Thur, 4/2/87
*We’re really going to enforce 65*

## Slide 18

**Notes:**
Slide of Interstate 25 SB in New Mexico with 75 mph speed limit, 1997.

## Slide 19

## Enforcement

- Integral part of the system
- Effect is limited
- Spatially
- Temporally
- Publicity campaigns
- Continuing deterrence
- “New” technology
- Traffic calming

## Slide 21

## Slide 22

**Notes:**
One of four 140 mph “White Hawk” mustangs purchased by the Albuquerque Police Department to enforce urban Interstate speed limit of 55 mph.

## Slowing Down Traffic

- Slowing Down Traffic

## Judicial Issues

- Limits must be perceived as reasonable and enforceable
- Primary consideration is safety
- Consistent treatment of violators
- Reduce court load through automated enforcement

## Technology Improvements

- Variable speed limits
- Photo radar
- Legal changes
- Public support
- ITS
- Information communication
- In-vehicle control

## Conclusions

- Safety, travel time trade-off
- One size doesn’t fit all
- Little basis for quantifying speed limit effects on
- Driving speeds
- Safety
- Speed zoning process
- Involve enforcement in the decision making

## Slow down or else

## Slide 28

## If All Else Fails

- If All Else Fails

- WHEN YOU
- DRIVE

- WHO GUARD
- YOU

- ANGELS

- USUALLY

- RETIRE AT
- 65

*Burma-Shave*

## Slide 30

**Notes:**
Time to stop this presentation and give the audience a break!