Day: 2015-08-10

Pavement markings near Green Line platforms aim to steer pedestrians clear of danger

| David Levinson

Tim Harlow at the Star Tribune uses my anecdote from a streets.mn post Do Not Wait Here (but does not link to it, as apparently must be Strib policy, lest someone think that there were other points of view on the internet). He did email to ask permission, to which I said: “I will just say you can quote my blog and there must be better designs.”

The article then misses the point that there is a design failure, and instead resorts to the standard official trope “Safety is a Shared Responsibility”, bureaucracy speak meaning blame the pedestrian. Of course pedestrians should behave better. But so should agencies. The LRT design, even more so than road designs from 1920s forward, is about reigning in pedestrians into fenced regions, so they do not interfere with the operation of the train. Designing a semi-permeable environment with multiple modes at multiple speeds and braking distances are difficult, which is why LRT is so, so dangerous compared to bus, but given current transit vehicle fetishes, one would hope the designers would get better with the actual design.

Paint is a wonderful thing, but self-explaining designs are better. A faux median is hardly self-explaining.

Elements of Access: Platooning

| David Levinson
Typical Signal Schedule and Traffic Flow Diagram, North-South across Market Street (San Francisco) (1929) From Signal Timing Schedule for Traffic Control Plan, June 15, 1929. Attempted "green wave": 8.5mph on Market
Typical Signal Schedule and Traffic Flow Diagram, North-South across Market Street (San Francisco) (1929) From Signal Timing Schedule for Traffic Control Plan, June 15, 1929. Attempted “green wave”: 8.5mph on Market
Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.
Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.

When you cannot go faster than the car in front, and you cannot pass them but you want to, you are joining a platoon. The speed of the driver at the front of this group of cars (which engineers evoking military organization call a platoon) imposes his speed on the others. While this may seem inefficient from your perspective, it may be to your advantage. Traffic engineers coordinate traffic signals so that if you are driving the speed limit, you make a series of green lights (this is called a “green wave”). (You are less likely to get a red light.) If you are in a platoon of vehicles arriving at an intersection, you are more likely to get a green light. If more vehicles are platooned on the cross-street, you will get more green time.