While the rest of North America, and most recently British Columbia, recognize the benefits of speed limits which reflect both the reasonable actions of the reasonable majority of the driving public and the safety improvements in modern day automobiles; Alberta bumbles along with speed limits which on some highways do not represent driving reality. The following correspondence was made recently between Jim Walker of the US-based National Motorists Assocation and the Alberta Minister of Transportation, Wayne Drysdale. If you live in Alberta and you are wondering why photo radar flourishes in Edmonton and Calgary, or why you have the speed limits you do, perhaps you will find this interesting.


Jim Walker, National Motorists Association

Dear Minister Drysdale,

Thank you for the response to my earlier email (copied at the bottom).

I must respectfully disagree with your conclusions that all of Alberta’s existing limits are correct to produce the maximum safety and smooth traffic flows.

Martin Parker (now with Wade Trim) definitively proved that 85th percentile limits were correct for urban environments in his 1992 study for the FHWA – the most exhaustive study of raising and lowering speed limits that was ever done – using about 100 locations.

www.ibiblio.org/rdu/sl-irrel.html     This study is the one mentioned in my original email and includes BOTH urban and rural segments. They do not behave differently in respect to 85th percentile limits. And the lowest crash rates were probable when limits were raised to or near the actual 85th percentile speeds of free flowing traffic under good conditions.

Also shown below is a statement prepared for the Chicago Tollway Authority by recently-retired F/Lt. Thad V. Peterson who headed the Traffic Services Section (the safety department) of the Michigan State Police for ten years. The statement was designed to try to persuade the Tollway Authority to stop defending their 55 mph posted limits on urban freeways where the 85th percentile speeds are 70 to 75 mph and the posted 55 represents a maximum compliance of 8%, with some segments having only 2% compliance.

Artificially low posted limits, those set more than about 3 mph or 5 kph below the actual 85th percentile speeds of free flowing traffic under good conditions tend to produce these results:  more speed variance, more passing, more lane changes, more conflicts between vehicles, more tailgating, more aggressive driving, poorer keep right except to pass behavior, and sometimes even more road rage.

These artificially low limits also tend to slightly raise the crash rates overall.

Correctly posted limits further tend to allocate more of the traffic to the best and safest roads.  Posting 85th percentile limits on the rural and urban freeways, rural and urban highways, suburban arterials and urban collectors – almost always the best and safest roads in their respective areas – tends to draw the highest proportions of traffic to those roads because drivers can then drive BOTH safely and legally at the normal traffic flow speeds without fear of speed traps.

Many US states have corrected their posted limits to be at or closer to the safety-optimum 85th percentile speed levels – with very good results.  Most Canadian Provinces lag far behind in this safety-improving method.

Posting speed limits that define 50%, 70% or 90% of the drivers under good conditions as violators destroys any belief that the speed limits are set for safety, damages respect for traffic laws in general as just being arbitrary, and destroys respect for the officers that enforce those artificially low limits for the only practical result of collecting revenue.

With VERY rare exceptions, main roads including the urban collectors and urban highways/freeways, should be posted at the 85th percentile speeds of free flowing traffic under good conditions. This method tends to produce the highest safety, the smoothest traffic flows, the greatest compliance by drivers, and frees traffic police to search out and cite drivers that are actually doing something dangerous — rather than being used for revenue collections.

James C. Walker
Life Member, National Motorists Association

Testimony for the Illinois Tollway Board

Meeting December 18, 2014

Madam Chairman and members of the board,

My name is Thad Peterson, and I retired from the Michigan Department of State Police in early 2013, after 25 years of service to the citizens of Michigan.

During the last 10 years of my career with the State Police I served as the commanding officer of the Traffic Services Section, where one of our main focus areas together with the Department of Transportation, County Road Commissions, and elected officials of all levels, was to correct hundreds of artificially low speed limits across the state.

The speed limit corrections implemented during my tenure in traffic services (mostly increases of up to 15 miles per hour) impacted millions of vehicle miles traveled per day. Over that same time frame, Michigan’s traffic fatality numbers plummeted, by about a third. In conjunction with my counterparts, I was recognized for those efforts with two Governor’s Traffic Safety Awards for Outstanding Contributions to Traffic Safety.

Many of these corrections were on urban freeways, typically correcting under-posted speed limits of 55 miles per hour to 70 miles per hour. 70 was the nearest multiple of 5 miles per hour to the 85th percentile speed, and closely matched the prevailing, safe traffic speeds on these freeways.

In all cases, we conducted after-studies to determine the effect of the changes, and to see if we needed to revise or reverse them. Safety was our overriding concern.

Despite our openness to adjusting our engineering changes or even completely reversing them if necessary, we found that our results were consistent with the long standing national studies on speed limit establishment:

  • No 85th percentile speeds increased by any significant amount, and some actually decreased after increasing the speed limit 15 MPH.
  • Overall, the crash rates on the freeways in question trended downward, and our fatality rate declined strongly statewide.

Rush hour traffic congestion on the urban freeway segments we corrected by speed limit increases, was dramatically reduced or eliminated.

Reduced statistical variance measured in the traffic speeds, matched the overall impression of greater vehicle speed uniformity, with reduced conflicts between vehicles and a more pleasant driving environment as a result.

The ONLY empirical measure that changed dramatically was a huge increase in compliance with the new speed limits.

As you would expect from these results, we never had to roll back any of the speed limit changes we made. With continued after-studies now many years after the changes, the results remain the same.

To summarize the dilemma related to speed limit changes, perceptions and expectation simply don’t match with the results.

People worry that vehicles/drivers will increase travel speeds by the amount of the speed limit increase. The best research solidly refutes this assertion, and in the hundreds of the road segments where we increased the speed limit up to 15 miles per hour, traffic travel speeds never increased significantly.

Travel speeds are made more CONSISTENT across the board, which is why crashes are normally reduced, and the crashes that do occur, do NOT tend to involve higher speeds than they did prior to the speed limit increase. The result is INCREASED SAFETY.

Road authorities are often concerned about an engineering factor called “Design Speed.” Interestingly, when citing this concern, they miss the point that if the speed limit is far below normal travel speeds for that segment of the roadway, they have usually already failed to design for the prevailing speeds at which traffic is traveling SAFELY. Design speed is a highly misused and misunderstood topic that should not deter road authorities from maximizing traffic safety through the use of optimal speed limits.

Upward speed limit corrections open the door for posting ADVISORY signs where road conditions warrant them, while increasing compliance with the speed limit. Artificially low speed limits, on the other hand, incite disregard for traffic controls as a whole, and DON’T allow for some advisory signs that drivers may really need in some cases to alert them to potentially hazardous design features of the roadway.

As you can see, there is much more to this extremely important, and somewhat counter-intuitive topic than time allows in this forum. I am more than happy to answer any questions you have of me, and I thank you very much for your time and your consideration of this topic that is of such great importance to the safety of your constituents and road users.

Respectfully submitted,

Thad V. Peterson, F/Lt., Retired
Michigan Department of State Police


—–Original Message—–
From: TRANS Minister <transportation.minister@gov.ab.ca>
To: ‘jcwconsult@aol.com‘ <jcwconsult@aol.com>
Sent: Mon, Jan 19, 2015 12:42 pm
Subject: Speed limits on Alberta’s roadways and recent developments in Michigan
Dear Mr. Walker:

Thank you for your email regarding speed limits on Alberta’s roadways and recent developments in Michigan.  As Minister of Transportation, I am pleased to respond.

My department’s goal is to provide a transportation system that is both safe and efficient.  I appreciate receiving your thoughtful suggestions and am always interested in hearing about best practices in transportation safety from other jurisdictions.  I am familiar with the Wade-Trim Report, and Alberta Transportation considers the 85th percentile speed and the design speeds of roadways when establishing speed limits on rural roads.  Roadways are designed so the 85th percentile speed is close to, but less than the design speed to allow for non-ideal driving conditions.  Posted speed limits are also set below the maximum design speed.

The Wade-Trim Report and the methodology are not as well suited to urban speed limits.  In addition to reducing the number of collisions on our roads, we are committed to reducing the severity of the crashes that do occur.  In urban areas, lower speed limits have been shown to help reduce the number of collisions causing serious injuries and fatalities.

Thank you for taking the time to write.  Feedback is always valued as I strive to improve Alberta’s transportation network.

Wayne Drysdale


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My original email dated December 14, 2014
To the Alberta Transportation Department:

One of the most important and most effective things the Department could do to improve safety and smooth traffic flows across the entire province would be to set almost all main road posted speed limits at the 85th percentile speed of free flowing traffic under good conditions, rounded to the nearest 10 kph (or 5 kph) interval.  Having posted limits no more than 5 kph from the safety-optimum 85th percentile speeds makes the limits as safe as they can be set.  This procedure is correct for both rural highways and freeways, as well as for the urban and suburban collectors and arterials that carry the heaviest traffic flows.

This known and many-times-proven 70+ year old method almost always produces the safest and smoothest traffic flows with the fewest crashes.  Traffic engineers and police officers with even a short time on the job know that posted limits have almost no effect on the actual traffic speeds, particularly for the drivers in about the top half of the speed distribution.  Raising or lowering the posted limits by up to 24 kph (15 mph) changes the actual 85th percentile speeds by no more than 5 kph (3 mph), and on average by about 1 or 2 kph (1 mph).
www.ibiblio.org/rdu/sl-irrel.html  ; A super-majority of drivers (85%) drive at speeds they find to be safe and comfortable, and which ARE safe and comfortable.  This super-majority chooses speed limits more accurately for safety than any arbitrary number.

Note that the author, Martin Parker, also produced a study on the recommended changes in posted speed limits for British Colombia dated 2003, about a decade before they actually adopted the more engineering-correct limits.  I would be happy to provide a copy if you don’t already have one in your files.

What 85th percentile posted speed limits do accomplish is smoother traffic flows with reduced speed variance, fewer conflicts between vehicles, reduced passing, reduced lane changes, reduced tailgating, better allocations of traffic volumes to the safest types of roads, better “keep right except to pass” behavior on multi-lane roads, and significantly fewer reasons for aggressive driving or road rage to occur. Typically a few of the faster drivers will slow down a bit perceiving the limits to be reasonable, and many of the slower drivers who were closer to complying with the under-posted limits either for fear of tickets or because they incorrectly believed it was safer to travel at speeds well below most of the flow will speed up a bit, and the entire flow gets smoother and safer.

Are there some exceptions?  Yes, including things like special limits for school zones that apply briefly at the times children are likely to actually be present.  Having statutory limits of 50 kph in areas that are truly residential makes sense as well, though those limits should not automatically apply to the collectors that go through or between subdivisions. Those streets should have 85th percentile limits to both make the flows safer and to encourage more traffic to leave the purely residential streets as soon as possible in favor of the collectors.

It is also necessary to have clear warning signs and advisory speeds for short distances for hidden hazards that are not apparent to the average driver.  Note this does not include things like high pedestrian or bicycle traffic, parked vehicles, large numbers of driveways or other access points, stop lights, stop signs, etc.  These items are visible to drivers and are already factored into their choices of safe and comfortable speeds up to the 85th percentile levels.  It is also incorrect engineering to lower the speed limit for a segment of road where the lower limit is needed only for a short distance near the hidden hazard.

A serious safety advantage to 85th percentile posted speed limits is the better direction of police resources to seek out and cite the drivers that are actually causing safety hazards, including those far enough above the normal speed distribution that their speed alone constitutes a hazard.  When posted limits are set 10, 20 or in some cases even 30 kph below the actual 85th percentile speeds of free flowing traffic under good conditions (which is far too common in Canada and many US states), there is too much tendency to allocate many of our scarce police resources to ticketing perfectly safe drivers going safely along with the normal flow around the 85th percentile speed range.  Note that these drivers near the 85th percentile speeds actually have the lowest possible risks to be be in or cause crashes.  It is counter productive to safety and a waste of highly trained police resources to ticket safe drivers.  Enforcement of under-posted speed limits is also the main cause of a loss of respect for speed limits, for traffic laws in general and for the officers that enforce them. This very serious problem started in most areas with lower posted speed limits to save fuel during the 1970s Arab Oil Embargoes, and is still not corrected today in many areas, some 40 years later.
The Traffic Services Section of the Michigan State Police (safety department) produced a Powerpoint presentation titles “Establishing Safe and Realistic Speed Limits” for the House and Senate Transportation Committees to explain how and why 85th percentile posted limits are almost always the safest ones to post.  A copy is on our website with permission as the last article here:


Please note that the command officers in this department received a Governor’s Traffic Safety Advisory Commission Award for their work in establishing realistic 85th percentile posted speed limits on many state and country roads all over Michigan.  I talked recently with one of them and he said they have corrected hundreds of posted limits to be up to the 85th percentile speeds, but never had to roll one back due to poor results.  Another of the Governor’s awards went to them for better rules to establish realistic work zone speed limits that get far better compliance for safety [45 mph Where Workers Present on freeways].  I have worked closely with this department for about 20 years. When they and the National Motorists Association both testify for or against bills in our state legislature, we could almost always trade our prepared statements because we both believe the same engineering science.

Alberta could make a significant improvement in safety and smooth traffic flow by reviewing all the main road speed limits and correcting those that are more than 5 kph below the safety-optimum 85th percentile speed level.  If you adopt this safety improving procedure, it would be helpful to produce something like the Michigan State Police piece mentioned above to explain the science to the public.
Respectfully submitted,

James C. Walker
Life Member, National Motorists Association
Board Member and Executive Director, National Motorists Association Foundation

Jim Walker Biography:  Age 70, licensed for 54 years, over 1.7 million kilometers of driving experience in 24 countries, a volunteer student of traffic safety and enforcement issues for over 50 years since my freshman year at the University of Michigan in 1962/63, a life member of the National Motorists Association, Board Member and Executive Director of the non-profit National Motorists Association Foundation, a frequent representative of the NMA to testify at legislative committees in the Michigan Legislature on all motorists issues, worked with the Michigan State Police command officers for over 20 years to work for realistic traffic laws enforced for safety and not revenue purposes, represented the NMA to testify at legislative committees in Pennsylvania, Ohio, and the city of Pittsburgh.