Tuesday, August 9, 2022 Aug 9, 2022
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Why Do Cars Drive Fast?

A question arose in a meeting the other day regarding, the how/why/and when cars drive fast or when they don't. The answer is that vehicles will drive as fast as they feel comfortable and the road will allow.
By Patrick Kennedy |

A question arose in a meeting the other day regarding, the how/why/and when cars drive fast or when they don’t.  I gave a bit of a rambling answer in too much detail about narrowness of travel lanes, amount of travel lanes, whether the road was one-way or two-way, etc.  It was all probably too much detail for such a meeting when the real answer can be summed up with an overarching theme:  vehicles will drive as fast as they feel comfortable and the road will allow.

Regulation (speed limits) and enforcement (ticketing) have minimal effect and are a waste of resources.  Engineered calming devices range from the expensive (raised cross walks, textured paving) to the ugly and annoying (speed bumps), but all are evidence of a poorly designed street where tension exists between how the street is designed and how the locals actually want and need the street to behave.

At the end of the day, it all comes down to the perception of risk.  How much risk is there to you (the driver), your car (in case of an accident), or in some cases others around your car including pedestrians.  But, since you are behind the wheel, at that moment your worst possible reptilian-brained self, you are probably less worried about the pedestrian’s well-being than your insurance premium and having to clean viscera out of your freshly detailed chrome grill.  The dehumanization of our road networks takes the enlightened out of self-interest.

The amount of activity around your car is what determines that risk.  Therefore, you slow down.  You make eye contact with pedestrians and other drivers.  All of a sudden, the ‘high risk’ streets actually perform better and are more safe.  Modern traffic engineering aims to mitigate that risk.  But what if risk makes streets better?  Trees are “fixed hazardous objects.”  Pedestrians create unexpected “conflict points.”

The amount of activity is something that is designed into a street and its street network.  Both of those have to be designed well in order to optimize place.  For example, the typical high street is the hub of the network.  A convergence point for activity and thus the opportunity exists for markets to emerge, social and economic exchange to happen – the fundamental purpose of cities.

The impulse of modern traffic engineering is to improve traffic flow on this high street.  All of those pedestrians populating the street, giving life, and patronizing businesses get in the way.  So roads are widened, sidewalks reduced.  More space is made available for cars.  The road then fails from a detailed road design perspective.

Afterwards, business begins to fail.  To make it better, we apply the same logic:  how do we get more cars there?  Buildings are razed to make way for parking lots.  Limited access highways meant to deliver more cars only fragment the grid and thus the network design fails.  Then your downtown fails.

A popular place first becomes invaded by cars, then abandoned, unless you make it amenable and accessible to pedestrians.  The accessible part is important.  If a place isn’t able to be walked to from short trips away, meaning people live nearby, or at least reached by transit, and the means of that trip by foot are safe, comfortable, and enjoyable for all ages, then it will in all likelihood fail to some degree as well.

Ben Hamilton-Baillie is a traffic engineer in the UK who learned under the tutelage of the late Hans Monderman, the father of the ‘naked street.’  A naked street is a street without any signage.  In his presentations, Baillie often quotes Monderman in his dutch-english accent, stating that “god will not save you.  You have to learn to fend for yourself.  Isn’t it great?”  Like any modern greek tragedy, he’s referring to god as modern institutions, in this case it is signage, over-engineered, and “improved” modern road design.

Baillie uses the metaphor of public ice rinks to convey how a great street should function.  All ages and skill levels interacting in a way that creates an order out of seeming chaos (without tens of thousands of deaths each year), pointing to a place in London called Seven Dials as one of the prime examples:


In the U.S. some places may not be ready for the shared space concept as espoused by Monderman and Baillie, who rightly use human behavior to guide their design rather than traffic engineering theory.

But we can calm traffic speed to safe levels while often improving traffic flow simply by redesigning our streets with ideas like road diets, where the amount of travel lanes are reduced to include space for parking (a buffer for pedestrians and a calming device) is included, as well as widened sidewalks and occasionally bike lanes if space permits and demand warrants.

A newly published 20-year long study of 4-lane to 3-lane road diets (third lane is a shared turn lane to avoid backups from left turns) in Portland shows significant reduction in traffic collisions.  Traffic volume was reduced slightly, but in all likelihood was made up for by increased pedestrian and bicycle traffic from a business activity standpoint.  Bicyclists and pedestrians tend to populate businesses more readily and easily since they’re not scouring for parking and are typically coming to this place as a destination rather than merely moving through.

Unfortunately, all too often our roads in DFW fail from both a street design and a road network perspective.  The places that succeed, the places that we love have been successful gaining marginal victories against the overwhelming orthodoxy of modern traffic engineering.  Some had success embedded in them historically (like Main, Bishop, and Greenville).  We just had to restore the street design to match the network.  Others have been successful by getting the street design right but being ‘off-center’ town centers like Shops at Legacy or Southlake Town Center. To get it entirely right and build a truly world class city, we need world class streets and street life. We have to embrace the reformation.



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