Monday, December 31, 2007

Caltrans response to questions about bicycle detection

I recently received a letter from Caltrans in response to questions that I sent them on October 28 about bicycle detection. I am concerned that although they say they will be installing bicycle detection at new and modified traffic actuated signals, their only options are Type D loops and video detection. They totally ignore my October 16 presentation to their Electrical Systems Branch on detecting bicycles with loops that, among other things, recommended larger loops and the use of bicycle detector symbols. Furthermore, they plan on doing no more development work on in-pavement detection (loops) and to concentrate on video detection. That means that any progress on improving bicycle detection at existing signals with inductive loops is years, if not decades in the future. Finally, they are concentrating on detection methods that differentiate between motor vehicles and bicycles rather than on detecting bicycles in the first place. They are not taking first things first.

The letter says that they will be adding a Discussion Item to the January 2008 CTCDC meeting agenda. I think that we should have some representation at that meeting to try to change Caltrans' direction and to get them to do some development work on inductive loops. I will be contacting the secretary of the CTCDC about giving a short version of the presentation that I made to the Electrical Systems Branch, focusing on my recommendations to Caltrans.


Bob Shanteau
Consulting Traffic Engineer

Robert M Shanteau, PhD, PE
13 Primrose Cir
Seaside, CA 93955-4133
Voice: (831) 394-9420
FAX: (831) 394-6045

Bicyclists and the basic speed law

Here is a letter I wrote to the editor of the Almanac-News about the
basic speed law. It was indeed published. [I have made some minor editorial changes in this version.]

Too often we hear about crashes between motorists and bicyclists in which the cyclist is severely injured or killed. And when that happens, we also hear about residents of Woodside and Portola Valley complain about how bicyclists on narrow roads with blind corners represent a hazard to motorists.

I am a traffic engineer and a traffic safety expert. I have testified in many traffic accident cases in which motorists have unknowingly violated what is called the basic speed law. The California Drivers Manual says the basic speed law "means you may never drive faster than is safe for current conditions." The way this law applies to narrow, winding roads is motorists must not drive so fast that they cannot stop in the distance
that they can see ahead.

As you drive, imagine that just beyond the point that you can see there is a stationary obstruction in the road (perhaps a log or worse, an injured child). You must not drive so fast that you cannot stop before reaching the obstruction. It does not matter whether the obstruction is hidden due to a curve in the road or the crest of a hill, you must be able to stop. It also does not matter if the posted speed limit is higher or if your car can handle the road at a higher speed. You simply should not drive faster than is safe considering the distance you can see.

Those drivers who say that bicyclists in the road are a hazard because they are surprised by the cyclist and forced to take evasive action are violating the basic speed law. After all, the cyclist is legally allowed to take the lane when the lane is too narrow to share side by side with a motor vehicle. In fact, the legally riding cyclist is traveling in the same direction as the motorist, which provides even more time and distance than would a stationary obstruction in the road.

Bicyclists depend on the good judgment of motorists for their very survival. Cyclists are not interested in assigning blame in the case of an accident. They want the accident not to happen in the first place.

Bicyclists need for motorists to respect their right to use the road and for motorists to share the road in a safe manner. And that includes limiting their speeds in corners and over hills so they can stop if need be, according to the basic speed law.

Sprawl vs crowding

The issue of density vs city size is a common problem that transportation planners face. Most people think that the answer to highway congestion is lower densities. In reality, the larger the city, the larger the benefit of high densities, but less highway congestion is not one of the benefits. It's hard to wrap one's head around the issue in the general case, so a simplification helps.

Imagine a city that is circular in shape with constant population and job densities throughout. (This is an idealized example of sprawl.) The average commute trip length depends on the distance between home and job. For a given population, lower densities mean a larger diameter city, thus longer trip lengths. Longer trip lengths mean higher flows on each link of the transportation network. If the transportation network consists of roads and people travel in cars, that means a lot of cars going larger distances. These cars need to cross each others' paths, and there are also natural and man-made obstacles, resulting in bottlenecks. The longer the trip length, the more bottlenecks a driver must pass through, with higher levels of congestion at each bottleneck. Longer trip lengths make walking, bicycling and mass transit impractical.

On the other hand, imagine the same shape city with a larger population density. Now the diameter of the city is smaller, homes and jobs are closer together, trip lengths are shorter, and people must traverse fewer bottlenecks. As a side benefit, shorter trips mean that more trips can be made by walking and bicycling. A higher density also means that mass transit is more practical, because mass transit depends on masses of people wanting to use the same route. If a lot of people try to drive
cars, they will get in each others' way, but they don't need to drive to get to where they want to go if they can walk, bike or use mass transit.

Now imagine a dense circular city with all the jobs in the center of the circle. Now mass transit is extremely practical, because everyone travels to the city's core in the morning and back in the evening.

I have lived in small cities with moderate densities where travel was easy. I have also lived in much larger cities with about the same densities, and in these cities travel was very difficult. I have also traveled in San Francisco during rush hour and seen for myself the benefits of a dense urban core.

Note, however, that a city such as San Francisco with high densities and large size does not necessarily have low levels of highway congestion. It does not take very many cars to congest a highway network, and the advantage of high density is not to decrease highway congestion but to make travel easier by making trip lengths shorter.

A dense urban area needs to be planned that way from the beginning, with high capacity mass transit, walking and bicycling included. In particular, building high capacity mass transit as an afterthought is extremely expensive and disruptive.