Topics: Pedestrian Facilities: the give and take between pedestrian and vehicular design.
Talking Traffic Episode 6 – Pedestrian Facilities: The Give and Take between Pedestrian and Vehicular Design
Welcome to episode 6 of talking traffic, the podcast devoted to bringing some of the dark details of traffic and transportation engineering into the light of public discussion. I am your host, Bill Ruhsam, and this is my podcast. Today is Monday, November 12th, 2007 and boy are my legs tired. I am training for the Tulsa Route 66 half marathon on November 18th, which is only 6 days away. Training for runners like me involves running three to four times a week with one long run on the weekend. Yesterday’s run was 12.1 miles. I hate running on treadmills, so I run outside, on, next to, and across an enormous number of structures that are designed (both poorly and well) to accommodate pedestrians. I thought I would talk today about how pedestrians affect transportation planning and design.
In the United States, with very few exceptions, pedestrians are an afterthought when it comes to transportation facilities. They are decidedly second-tier citizens. From a traffic engineering standpoint, pedestrians are hell on traffic flow. For one thing, they are slow. For another, there generally aren’t very many of them. For a third, when they do get into a collision with a vehicle, they generally die. These are all bad things. A self-respecting pedestrian should know enough to go home, get into his car and gosh darn it, Drive! wherever it is he’s going. This has been the prevailing roadway design philosophy with respect to pedestrians for a very long time. The thrust of 40 years of effort has been for more vehicular mobility, more throughput, less congestion, higher traffic volumes, quicker commutes, better quality of drives. Nowhere was there room to fit the 150 pound sack of blood and flesh that doesn’t react well to the impact of 2 ton cars. Notable exceptions to this policy are the extremely dense older cities of the east coast with developed public transit systems, plus newer designed communities specifically built to accommodate the co-existence of people and vehicles. Notable adherents to the code “car is king” are the sprawling subdivisions of the United States western states where all there is is room to expand. The reasons behind the universal focus on automobiles are numerous and cross all boundaries of politics and culture in the US. The cultural focus on the automobile as a symbol of freedom is one, federal legislation that doesn’t give the same sort of incentives toward construction projects focused on pedestrians are another. The general lack of transit usage is a third. The causes behind these cultural artifacts are legion, and fill many a graduate dissertation. I’m not here to discuss them, because I’m no expert. I am here to discuss how they have affected transportation facility design.
Pedestrian facilities were often an afterthought during the race to build more and bigger subdivisions during the latter half of the twentieth century. Within housing developments, where vehicular speeds are slow and neighbors generally respect each other, there wasn’t much need for well-designed sidewalks, ramps, and crosswalks. If all else failed, you could trundle along the side of the road with safety. This premise collapses when you start walking along high-speed, high-volume roads that are built to move people expeditiously from home to the Piggly Wiggly and back. To facilitate pedestrians here, sidewalks are constructed adjacent to the roadway, out of either concrete or asphalt (sometimes brick). The smooth surface allows people to stroll along without too much consideration for where they are stepping, unlike walking on the shoulder of a roadway. This is the easy part. More complicated is where people must interact with the 2 ton steel people-flatteners. We call these grinding mills of people-destruction, “Intersections.”
Intersections have many design features that can go toward making either the vehicle’s life easy, or the pedestrian’s, but not both. For example, how wide the corner radius of the turn is will directly effect how fast a vehicle can navigate the turn: the wider it is, the faster they go. But, the wider the turning radius is, the farther pedestrians have to walk to cross the road, and they have the delightful experience of needing to dodge vehicles that are making high-speed right turns without seeing that pedestrian that just stepped off the curb. Very narrow curve radii will permit a pedestrian ample visual warning of approaching vehicles and a shorter distance to cross the roadway, but they are difficult for vehicles (especially large ones) to negotiate, and therefore reduce the vehicular capacity of a roadway. Pedestrian crossing signals also adversely effect vehicular capacity in many cases. For example, let’s imagine the high-speed suburban arterial I mentioned above. There are 3 lanes in each direction with a raised concrete median between them. Traffic zipping along is dense enough that you can’t cross without becoming road pizza, so you walk to the nearest cross street with a signal. This cross street is a road coming out of a local housing development and is only two lanes. When you arrive at the signal there are two cars waiting for the green. Just as you arrive, the arterial signal turns amber, then red, stopping the 500 or so vehicles who were moving along toward Starbucks. The cross street signal, as well as the pedestrian signal you came here for both turn green (white for you) and you proceed to cross the 6 lanes (plus median). The 2 vehicles waiting at the cross street take about 8 seconds to get through the intersection, but by that time you are only about halfway through the third lane. Another 8 seconds and you’ve just entered the fourth lane after crossing the median. Another 8 seconds and you’ve finally stepped onto the opposing curb, the cross street traffic goes red and the (now 1000) anxiously waiting mainline vehicles lay a patch on the way to their caffeine fix. What did that narrative demonstrate exactly? That as soon as you insert pedestrians into a traffic stream, you need to account for their different speeds. While the cross street vehicular traffic was served in 8 seconds, it took you, the pedestrians, 24 seconds to cross the street. That is an absolute minimum time, at 4 feet per second, which is a standard speed used to calculate pedestrian signal timing. Of that 24 seconds, 16 of them were not being used to serve vehicular traffic, which makes your standard American suburban driver cranky when she sees no pedestrians. This is an extreme example, of course. In these circumstances, the pedestrian signal wouldn’t be activated unless the pedestrian pushbutton were pushed, but if that button breaks, or is vandalized, it will continually call for that 24 second pedestrian interval. Again, this is an illustration where pedestrian needs and vehicle needs are in direct conflict. This example is particularly strong because if you consider the case where you , the pedestrian, only wanted to cross the cross-street, you’d have time and plenty left over, because the main line street will have upwards of 60 seconds on it’s green time, giving you enough time to cross the two-lane cross road 10 times! What this leads to on a day to day basis is calls to the city/county/state traffic engineer from irate drivers demanding to know why they are waiting so long at that intersection when there’s nobody there! This puts pressure on designers to leave out the pedestrian elements entirely, to avoid the situation and allow the pedestrians to fend for themselves.
Of course, there are compromises that allow the two travel modes, vehicular and pedestrian, to coexist without overwhelming our transportation infrastructure. In the previous example, where you were crossing the six-lane roadway, a solution could have been to have the pedestrian cross to the median, then wait for the next cycle before crossing the rest of the way. Or, in a high pedestrian traffic area, a pedestrian bridge could be constructed. There are numerous complexities associated with pedestrian traffic which I won’t get into right now, but keep in mind that everything I’ve discussed so far only applies to a pedestrian who has their full faculties. In other words, not blind, not deaf, and not in a wheel chair. As soon as you introduce those elements to the mix, we jump into the hyper drive of pedestrian facility complexity. For example, within pedestrian facility design, there are structures that are mutually exclusive between the blind and the wheelchair-bound. But this podcast is already getting a bit long-winded.
To end, I have advice for those of you who are out there, on our American roadways, without the protection of airbags and crumple zones. As I mentioned above, I spend time on my feet, negotiating with traffic around my neighborhood. The most dangerous places I run through aren’t the huge 6 lane crossing 6 lane intersections, it’s the smaller two lane with two lane stop-controlled ones. This is because of several reasons. For on thing, there’s no sidewalks in these areas (or I don’t use them, to avoid pounding my joints on concrete). For another, drivers around here just aren’t used to seeing pedestrians therefore don’t look for them. Also, as a pedestrian, I’m on defcon 1 when I’m at a huge high-speed intersection, but much more likely to be zoning out to my Ipod when I’m running through a tiny four-way stop. Do everyone a favor: Run or walk against traffic; don’t turn up your music so loud that you can’t hear traffic noises; wear light colored or retro reflective clothing; and please pay attention. Pedestrians have the right of way everywhere, but as my dad always used to say to me when we were crossing A1A in Florida to get to the beach, “You might be right, but you also might be dead right”
This episode of talking traffic is distributed under a creative commons 3.0 attribution, non-commercial, no derivatives license. Despite the fact that Author Michael Stackpole eschews the used of the creative commons, maintaining the opinion that everything that is covered in creative commons is covered in the Bern Convention of copyright, I personally endorse the spirit of creative commons, which emphasizes different levels of creative control. You can use this podcast in its entirety, and redistribute it without my permission, because I’ve already given it! Just make sure you don’t change it, don’t sell it, and credit me and talking traffic.org.
As always suggestions and comments are strongly encouraged. You can leave them on the show notes at www.talkingtraffic.org or send me an email at bill at talkingtraffic.org. Music today was by Beight and they can be found at magnatune.com. I hope you enjoyed this episode and please, don’t become road pizza.
Music: Beight at magnatune.com