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March 08, 2006

Ramp metering the Louisville area

One of the things I dread about going downtown in the mornings is the drive. With Louisville, you never know what the traffic is going to be like from day to day. Some days, it flows smoothly with no problems at all. Other days, the traffic can be backed up from Blankenbaker all the way down to the downtown area.

Every morning I grit my teeth as I near the ramp on Blankenbaker heading West towards downtown. It's always a gamble on what I'll see upon my arrival. Most days it's generally OK, with only a slight buildup of traffic up till the Hurstbourne exit.

That's when it gets *UGLY*.

The problem with the traffic flow in Louisville, at least on I-64 West in the mornings, is due mostly to the ramps. Hurstborne has a two lane ramp that spills a significant amount of traffic onto I-64 all at once at regular intervals. These people then make a mad dash to get over to the left lanes so that they won't get locked into merging with the Watterson ramp a few miles down the road.

The two-lane ramp at Hurstborne (westbound at the top of the image).

All of this craziness causes the rest of the traffic to slow down a considerable amount on almost a daily basis.

And once you're past Hurstborne, there's Cannon's Lane. This section of I-64 may be even worse than Hurstborne on some days. The problem here is that you have a one lane ramp that is feeding a large amount of traffic every 20-40 seconds onto a 2-lane Interstate. The resulting mass of vehicles causes all traffic in the right hand lane to physically come to a stop to allow traffic to merge from the ramp onto the Interstate. People try to avoid this by getting over to the left lane, but this only serves to slow down traffic on the left lane as well ... if not causing it to come to a complete halt all together.

The Cannon's Lane ramp. It spits traffic onto the Interstate without much runway.

There are other ramps on I-64 heading downtown that spit out traffic as well, but I would honestly say that these two are the biggest culprits.

Last November, I was required to take a trip to the Phoenix area to do some network router installations. This trip required me to be on the Interstate in the Pheonix area alot, and I noticed that even though the city is considerabily larger than Louisville, they didn't see the ramp slow-down that I witnessed on a daily basis here at home. The reason for this was due to something called ramp metering.

The concept is simple.

In order to keep Interstate traffic flowing at an optimal rate throughout the entire day, regardless of rush hour traffic or not, off ramps throughout the city use ramp meters. Typically, what you would see would be a two-lane ramp with what looked like a stop light at the end on both lanes. There was a green light and a red light. These lights would alternate in a way that caused traffic on the ramp to stop for a brief period of time, which averaged out to be about a second or two.

As the lanes would alternate, each lane would allow one car to move forward off the ramp to a single lane road that would extend for roughly 1/4 of a mile. This would give the vehicles that were coming off the ramp enough time to speed up and make a safe merge into the oncoming traffic already flowing on the Interstate. As a result, traffic that is already in motion on the Interstate isn't required to slow down to allow traffic from the ramp to enter onto the road.

Phoenix metered ramp. Circled in orange is the meter.
Circled in green is the long ramp.

Now, this didn't mean that the meter system was on all day throughout the day. During late night or later evenings, when traffic was significantly lighter, some of the meters would shut down, allowing the traffic from the ramps to flow steadily out of the ramp onto the Interstate. In heavily trafficed areas, they would stay on throughout the day to help regulate the traffic flow.

This, to me, is a fantastic concept. The ramp from Hurstborne onto I-64 is already set for using a system like this as there is a few miles between the time one would enter the Interstate to where the ramp to the Watterson begins. All that would be required was two meter lights on either side of the ramp prior to the traffic merge onto I-64 set to alternate, just like the meters did in Pheonix.

The ramp at Cannon's Lane, however, is a different deal completely. It is also part of the problem that causes traffic to back up. The ramp, as it meets the Interstate, is only a few feet long. There is no way for any vehicle coming off of the ramp to successfully meet the speed of the traffic on the Interstate to successfully merge once a vehicle had been released by the meter. This means that the ramp coming from Cannon's Lane to I-64 would need to be extended by at least 1/4 mile for this to work successfully. Also, considering the amount of traffic that builds up on this ramp, I think that it would make sense to also make this a two lane ramp as well to hold up the queue of traffic that is sure to build.

This is something that I have been thinking about for a few weeks now and have been wanting to put down to paper for others to read. Now that I've done it, I'm curious to see what other people think about the concept. Personally, I would love to see the Mayor and several city council members hop on a plane and head to Phoenix to drive around for a while and get a feel for the idea.

On an interesting note, I did a Google search for the terms "ramp meter" and "louisville" to see if this is something that anyone else has blogged or if any government Website had records of consideration for ramp meters in Louisville. My search came back with nothing of interest.

~out...

Posted by ed at 09:13 PM | Comments (2)