Colorado Highways:
Ramp Meters

Like other metro areas in the US, CDOT uses ramp meters to manage traffic on the freeway system. For those who don't know, a ramp meter is a signal part way down a freeway onramp that is red part of the time and turns green at intervals, usually allowing one vehicle per lane at a time through, to manage the amount of traffic entering the freeway.

Ramp meters can be looked at as doing two things: 1) They prevent traffic from entering the mainline in large clumps all at once, improving the performance of the merge area, and 2) can also be used to proactively restrict the number of vehicles entering the mainline to keep it from reaching capacity. The overall theme is that the people on the ramp are being sacrificed (by making them wait longer) in order to improve the performance of the mainline.

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In Colorado, CDOT ramp meters are usually placed on two-lane ramps so that when the meters are on and queues form there are two queues of cars. "Signal ahead" signs with "WHEN FLASHING" plaques advise motorists when the meters are on. The meters themselves are made up of a red-yellow-green signal pointed up the ramp and a red-green signal pointed inward so drivers at the stop bar can see it.

Meters are dark during off-peak hours when not in use. During normal operations the signal only flips back and forth from red to green; yellow is not used. Flashing yellow is used for a brief period when the meter first turns on. The hours the meters are on varies widely from location to location; some are all day, some are rush hour only. Some will be on at an interchange and the next interchange a mile down the road they won't be on.

One beef I have with how CDOT operates the meters is that the meter for each lane turns green at the same time, rather than being staggered. The result is almost a game of chicken as each driver screams out of the starting block to try to be first to get to the point where the ramp tapers back to one lane.

In Colorado, ramp meters are used on most of the freeways in metro Denver. Nearly every interchange along I-25 and I-225 has them, plus numerous interchanges along I-70, I-270, US 6, US 36 and C-470. Outside metro Denver there are meters at several I-70 interchanges in the foothills west of Denver.

A typical CDOT ramp meter, at the northbound onramp to I-25 at Evans Avenue as it appeared before T-REX construction.


Created 13 May 2001
Last updated 18 March 2011