Tom Philois annoyed with . . .

Metered On-Ramps

To Solve A Traffic Problem

The latest craze for traffic engineers is to install onto every freeway on-ramp entrance traffic signals. They are known as "Metered On-Ramps".

This craze has been going on since the late 1980s but have really become prevalent since the mid-1990s all over the USA.

The idea is to regulate the incoming traffic flowing onto the freeway in a timed controlled manner. This engineering solution theory is that by regulating the flow of all vehicle traffic onto the highway, by forcing the new traffic to wait a set timed interval, it would prevent bunching up of incoming traffic thereby spacing the new cars out allowing them to find space (holes) in the existing traffic flow in a steady manner. The old method allowed bunches of cars (platoon of cars in traffic speak) entering the highway at the same time where they all cannot find holes in the traffic lane and thus be forced to stop blocking the acceleration lane. Thus, the timed release of vehicles will keep the traffic flow at the same speed and generate a hole to be found to allow the car / bus / van / truck to safely merge into the stream. This would avoid slowing down the existing traffic. This would ensure that the overall speed of the highway stays up at the limit allowing more throughput on the road.

This is only a theory.

The Reality of Traffic Lights on On-Ramps

In reality, the road they are trying to enter is so overloaded that it just makes people wait one to two minutes (sometimes 10 minutes) longer to get onto the road.

It also costs around $250,000 per intersection to put in the lights.

The next time you get onto one of these metered ramps look at their design and see where they put the traffic signal lights. JUST before the acceleration ramp ends and merges with the highway.

This means each car must accelerate from a complete stop to 55 or 65 mph in 1/4 of a mile or less. Usually there is just 1/8 of a mile — 500 to 700 feet — in these now truncated acceleration lanes. The other 1/8 of a mile that was there is is reserved as a parking lot for the cars backed up waiting for their chance at the lights.

Driver Habits

Driver Education People - - at the urging of national safety institutes and insurance companies — have been instructing people for the past 30 years (and still do) to NOT stomp on the gas to avoid a "jack rabbit" start when driving. Other Federal agencies have campaigned to get drivers to accelerate slower in order to save fuel. Drivers are to use a slow and steady acceleration so that it takes them 20 to 30 seconds to get to highway speed which saves fuel.

This was done to increase MPG (miles per gallon) fuel efficiency in cars. MPG drops it to around 10 MPG or less when stomping on the gas pedal— but then the high fuel flow rate duration is only for 10 seconds! This argument is really meaningless as far as fuel efficiency goes. You recover the "wasted" fuel back since you get to cruise speed 15 seconds faster than a slow steady acceleration.

Thus since the 1970s people have been taught to go slow from a complete stop.

Ramp Length

The effect of slow acceleration means that using the existing educational methods it takes a driver at least ½ mile of roadway — anywhere from 15 to 30 seconds — to get to 55 mph. Since most on-ramps are only 1/8 of a mile long now due to the traffic lights and the need to have a place the for cars to queue up behind it, the cars are only going to be at best around 30 mph when the acceleration lane ends and they must be in the highway lane using the school taught methods.

So, as these people are doing only 30 mph as they merge into a 55 mph traffic flow something has to give way. People in existing traffic merge zone must either move left to allow the new vehicles into the rightmost lane (95% of drivers do not do this) or those right lane drivers MUST slow down to 30 when those on-ramp cars force themselves into the traffic flow — or else hit them.

This "human factor engineering" slows down existing car and truck traffic — exactly the opposite of the intent by the traffic engineers! These engineers expected that putting in the metered on ramps would accelerate traffic! This problem is what the meters are supposed to prevent!

Additional Costs

A vehicle is most efficient when the engine is running at its designed RPM in which the peak shaft horse power with the lowest fuel consumption exists which in turn translates into a given speed. Some cars are most fuel efficient at 65, some at 75, some at 40 and so on. No vehicle is getting good gas mileage when it is idling at a red light.

Now when you have 50 cars idling anywhere from two (2) minutes up to five (5) minutes at a time to get onto a road that is WASTING more fuel than the slow down that is allegedly caused by not having the meters. Now multiply this wait for the other 60 or 70 on ramps to highways in a small city like Portland, Oregon and you now have at any one time 3,000 cars idling during the two hour period of the morning commute. This is repeated again during the evening commute.

Add in the cost of putting in the lights, and the maintenance of them (computer personnel, traffic surveys, applications to federal funds to get more of them, doubling the lane width to handle more queue traffic etc.) and you can see how a place like the Portland Metro area can easily spend $70 million dollars putting up lights to make people wait to get onto the roads!

Road Capacity

Any given road has a fixed maximum capacity. This is computed by the speed that is allowed on the road by the number of lanes on the road.

If a road is set at 50 MPH then in any one hour one lane could theoretically handle 50 miles of cars going past a spot in one hour. Giving that a car takes up space (say 12 feet), and even with the best tailgater there is always space between cars of at least 30 feet when going 50 MPH, it means that every car takes up at least 42 feet of a lane. Divide 42 into 5280 and you get 125 cars per mile. This in turn is multiplied by 60 minutes and therefore 7542 cars could go past a point in one hour on one lane. So a two lane road set at 50 MPH should be able to handle 15,085 cars an hour.

As you move closer into a city on a road more and more people get onto the road. Thus that 30 feet of space now has a car where there was space before. So people slow down and create more space between cars. Thus the people have to slow down some, more cars get onto the road, more slowing, and so when you get really close to a city the capacity of the road that allows 15,000 cars is trying to handle 20,000 an hour and since people want to maintain some spacing all cars slow down and thus traffic goes slower.

Now the metered on ramps are ALWAYS near the city and so they are metering onto a road that is already over capacity. Thus the speed is already down and the ability to accelerate to get into the lane is no longer valid since people are only doing 20 to 30 MPH and there is even LESS space for them to get into. Going slower people close up to 10 or 15 feet spacing and so now people are having to force their way into the main road lanes.

Since the metered ramp lets a car go every 1 to 3 seconds expecting the main highway to be at 50 MPH or higher, and the traffic is going 30 MPH, they just go forward into a NEW queue trying to get onto the road and the whole idea of metered traffic on-ramps is just a waste of time, money and fuel.

Timing Note

When the ramps first turn on they usually (here in Portland Oregon anyway) let a vehicle go every three seconds. As rush hour builds they let vehicles onto the road every second.

Think about this.

When traffic is lighter they make them get on slower and when traffic is heavier they let them on faster.

Why?

Because if they did not cut the time down during rush hour the traffic waiting to get on would back up onto the side roads and block traffic on them!

Thus, by looking at the way they time the signals you can see that the solution they came up with actually solves NOTHING.

The studies done to justify this method were done where there is NO backup on the roads during the worse rush hour that road has ever seen. Thus the oncoming traffic has LOTS of room to accelerate up to speed, find a space to merge in and continue on. There is no bunching of cars one right behind the other trying to get onto the main road.(A bunched up ramp lane is always due to the first driver NOT accelerating fast enough to go from 0 to 50 MPH in 8 seconds in 1/8 of a mile.) One slow driver causes people behind them who do accelerate correctly to be 20 feet behind the slow one within 3 seconds so that within 6 seconds three cars are now are ready to get onto the main road and that means that an 80 foot gap in traffic is needed to allow all three cars onto the road at the same time without slowing down.

If the normal spacing is only 30 feet then the lead person either stops to wait a large gap, pulls out anyway forcing the traffic lane to brake to avoid a collision, swerve to another lane (if open) but usually they are forced to slow down and therefore now you have slow traffic the rest of the morning at the merge.

Once slow it never recovers till after the "rush hour."

Magentic Loops Sensors

Built into every ramp is a sensor that tells how many cars are on the ramp. This allows the computer to change the timing as the ramp / highway fills up to guess as to how often it should let cars onto the road and at the same time not allow cars to spill onto the side streets.

You can always tell that there are loop sensors by cuts in the pavement and the fact that if NO cars are on the ramp the light is RED. You are expected to come to a COMPLETE stop, wait 1 to three seconds, THEN speed up again.

This is pretty stupid.

They could save millions of dollars by just going back to the mechanical method of setting the light to go GREEN every 1.5 seconds and forget the idea of adjusting the release timing. It does no good anyway.

Course even more money would be saved if they just turned them off. At one ramp that routinely drive down the meter fails every once in a while and there is NEVER a backup on the road nor the ramp. When it is turned on some 60 cars are always in line (two lines).

Intersection Spacing

Major roads near cities usually have a merge lane every 2000'. (Federal highway standards have changed but usually major merges are only allowed no closer than every mile in cities, and 5 miles in rural areas.)

City and county rules regarding their road of course vary.

 

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