LEFT-LANE LAWS CAUSE TROUBLES

Laws Reserving the Left Lane for Passing
Harm Merging and can Halve Highway Capacity

EFFECT OF LEFT-LANE LAWS ON MERGES

LEFT-LANE LAWS CONCENTRATE TRAFFIC IN MERGE LANES, MAKING MERGES HARDER

A high concentration of vehicles in the merge lane means that merges are more difficult.

Rules of merging tell some drivers to move into lanes the merge does not enter.

VEHICLES MUST BREAK LEFT-LANE LAWS IF MERGE TRAFFIC EXCEEDS RIGHT LANE CAPACITY

After a heavy merge, there may not be enough room for all of the vehicles on the highway to obey the left-lane law. Traffic on the road may exceed the calculated capacity below.

Those cars will fit on the road, but they must break the left-lane law to do it.

LEFT-LANE LAWS MAKE VEHICLES WITH TRAILERS USE THE MERGE LANES

A vehicle pulling a trailer is too long for a merging driver to find a safe gap.

If a gap disappears ahead of a long vehicle, there is not time to get behind it before the merge lane ends.

Vehicles pulling trailers (including semis) should get out of merge lanes if possible. This includes semis.

Usually the stupid left-lane laws require these vehicles to be in the merge lane.

ROAD AND HIGHWAY CAPACITY

How many vehicles per hour can a traffic lane carry? The following table shows the numbers.

Notes:
- 2-second minimum safe following distance is used to get the 1800 veh/hr value.
- 3-second minimum following distance is needed above 45 mph, giving 1200 veh/hr.
- Two-way traffic capacity is reduced by left turns across oncoming traffic and waiting to turn.
- Use one-way capacity if the road is divided and the median has no openings.
- On-street parking reduces the capacity of the adjacent lane by 500 veh/hr.
- Multiply lane capacity by the portion of time the traffic signal is green to get the capacity through the signal.
- If two-way double-alternate signal progression is used, divide the signal capacity by 2.
- Roundabouts have a capacity of 1800 veh/hr total of all approaches.
- All-way stops have a capacity of 1500 veh/hr total of all approaches.

When traffic exceeds the capacity of the road, the speed goes way down to maintain safe following distances.

CAPACITY WHEN NOBODY IS PASSING

How many vehicles per hour can use a one-way highway when no vehicles pass other vehicles?

Each lane can carry 1800 veh/hr at speeds not above 45 mph.

Each lane can carry 1200 veh/hr at speeds above 45 mph.

CAPACITY REDUCTION CAUSED BY ONE PASS

How many vehicles per hour can use a one-way highway when one vehicle passes one other vehicle in that hour?

How much space is needed to let one extra car enter the stream to pass?
At least enough space for one car and its following distance is needed.

How much space is needed to let one car re-enter the original stream?
At least enough space for one car and its following distance is needed, since the original space vacated by the passing car is behind it.

Room is needed for one extra car in each lane involved to allow one car to pass.

Each car that changes lanes needs an empty space for one car to fit into in the lane it moves into.

In heavy traffic, the traffic in the other lane must make room for the passing car to enter the lane. This slows all of the traffic down.

CAPACITY WHEN ALL DRIVERS CONSTANTLY CHANGE LANES

How many vehicles per hour can use a one-way highway when all vehicles are constantly changing lanes?

How much space is needed to each car change lanes constantly?
At least enough space for one car and its following distance is needed for each car.
This assumes that all of the cars change lanes at random.
For all of the cars in the right lane to move to the next lane, either both lanes have only 900 cars each, or the next lane has enough space to take all of the cars in the right lane. If the right lane has 1800 cars, the next lane must be empty.

Room is needed for one extra car in each lane for each car in the lane.

There must be an additional empty space for each car on the road.

Whenever you pass a car in heavy traffic, it delays all of the cars behind you.

Whenever someone in front of you passes in heavy traffic, it delays you.

Whenever someone in front of you passes a vehicle going below traffic speed, nobody is delayed because a gap opens ahead of that vehicle.

In heavy traffic, everyone would get there faster if nobody on the road passed anyone else (other than vehicles going below traffic speed.

CAPACITIES WITH AND WITHOUT THE LEFT-LANE LAW

Notice that the reduction of capacity caused by the left-lane law is equal to the capacity of the left lane.

This is because, when nobody is passing, all of the traffic must be in the other available lanes. This means that ALL of the traffic must fit into the other lanes. So the left lane is effectively removed from the capacity of the highway.

When nobody is passing, all of the traffic must fit in the other available lanes. This law requires vehicles to stay out of the left lane unless they are passing or turning left.

Question: What happens when one car passing another comes upon a car that is turning left (or taking a left exit)? It definitely spoils the pass.

Where are those 1800 cars supposed to go?

It's time to get rid of the idea that passing other vehicles is important.

It's important only to selfish drivers who are in too much of a hurry.

But every time someone else passes in heavy traffic, it slows you down.