Monorail Alignment

by Bob Fleming

My opinions regarding alignment of the monorail in the street.

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The Controversy

There is some controversy over the alignment of the monorail, i.e. whether it should go down the middle of the street or on one side or the other. The arguments vary, depending on which part of which street, because the circumstances are different in different places.

My Opinions

I THINK THAT IN MOST PLACES THE MIDDLE OF THE STREET IS BEST. Most of the streets along the route now being designed, the Green line, are two way streets with two or more lanes in each direction and with a two-way left-turn lane in the middle of the street. Near some intersections the two-way left turn lane is replaced by a left turn storage lane for one direction only. There are also some streets that have a median strip of concrete, grass, plantings, a barrier, or a combination of these.

WHERE THERE IS A MEDIAN I THINK THERE IS NO CONTROVERSY. The median strip is the ideal place to locate the pylons (columns) supporting the monorail guideway. Nobody can make left turns across the median anyway, so the pylons can not interfere with left turns. As long as the median is wide enough, this is the place to put the pylons.

WHERE THERE IS A TWO-WAY LEFT-TURN LANE, I STILL THINK THIS IS THE PLACE. I see several advantages to using the two-way left-turn lane for locating the monorail pylons:

  1. The pylons will not interfere with through lanes of traffic.
  2. The pylons will not take away curbside parking space.
  3. The pylons will not interfere with pedestrian traffic on sidewalks.
  4. The pylons will not interfere with left turns except right by a pylon.
  5. The monorail trains will be further from buildings.
  6. The monorail structure will not interfere with trees planted alongside the street.

THERE COULD BE A PROBLEM IF THERE IS A LEFT-TURN STORAGE LANE. A left-turn storage lane is a one-way lane for cars that will be making left turns into an intersecting street. You can not block the left-turn lane with a pylon.

I know of two solutions: If the left-turn lanes are short enough, and if the intersection is narrow enough, you could span the entire intersection including the left-turn lanes with a long guideway beam. Otherwise, you could use straddle bents to support the guideway. Straddle-bents are beams like wide upside-down “U”s. They would span the same street the monorail is on in order to support the monorail guideway instead of a pylon. Straddle-bents are used to support part of the guideway of the existing Seattle Center Monorail where it makes the curve at Denny Way. They could be used in any location where it is not practical to put a pylon in the street. They are not attractive and cost much more than a pylon, but sometimes they are what is needed to do the job.

THERE COULD BE A PROBLEM NEAR STATIONS. In most cases the stations will be located on one side or the other of the street. Designers want to avoid locating a station over the street because it would block the sun and make the street too dark.

So if the station is to the side and the monorail is going down the middle, it would be necessary to curve the guideway over to the side for the station and then back to the middle the other side of the station. These extra curves limit the speed of the train. However I don't think this is a significant problem because the trains have to slow down near the station anyway in order to stop at the station.

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©2003 Robert M. Fleming Jr.

This page was last updated on 9 May 2016

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