Advanced Topics in Congestion

At the last TPAC workshop on the Regional Transportation Plan update, Metro presented their research on roadway conditions (freeways and arterials). There are some very interesting ways to visualize the situation.

[Note: click on any slide to see a larger (and clearer) version.]

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A table showing what portion of our freeway and arterial network is congested (at PM peak), by lane mile. A Volume/Capacity ratio of greating than 0.9 is generally considered congested. You get free-flowing traffic up to about 0.8.

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The table turned into pie charts.
Note that even though about 25% of the freeway network is congestioned, it’s only 11% or so for arterials. Most of our major road network is working!

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This chart shows congestion versus time of day. Regional policy says we should avoid getting congested in the red box (i.e., freeways should be relatively free-flowing outside peak hours, which is important for freight). We’re clipping the edges on I-5 Northbound.

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On the other hand I-205 seems to be working pretty well off-peak.

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This is a really interesting diagram call a travel time contour. The colors tell you how long it takes to get to the target location (yellow is about 25 min), in this case the Washington Square area. One of the goals for the scenario exercise in the RTP process is to show how these will change with different investment scenarios.

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This is for the Clackamas County industrial district.

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This diagram looks at congestions not as a question of travel time itself, but rather in terms of variability in travel time (or reliable). Part of the theory is that longer travel times may be acceptable, if they’re predictable.

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Travel times past Nybeg Rd. on I-5 seem pretty reliable.

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But Highway 26 is a crap shoot!

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