By Tom Symonds BBC transport correspondent

As investigations continue into the cause of the fatal school party coach crash in France, the European Commission is preparing to tighten the rules for long-distance bus drivers.

The current rules for multi-crew coaches are indeed complicated.

They permit a coach with two or more drivers to travel for 22 hours by alternating.

Each driver can only spend four-and-a-half hours at the wheel, before he has to take a 45-minute break.

He could also take breaks of 15 minutes within the four-and-a-half hours period, which can be taken on the coach while moving.

Katherine Fish, 15, died in the crash

After 22 hours the drivers must have eight hours rest away from the coach.

In practice the drivers would do four-and-a-half hours, then rest on the moving coach for the same length of time.

Some modern coaches have sleeping compartments for drivers, but most do not. Drivers take their shorter breaks in normal seats.

Very long distance coaches tend to pick up drivers along the way, to reduce the number of seats taken up by the crew. With a new crew, the coach can continue without a long stop.

Digital tachometers

The EU wants to cut the 22 hour maximum to 21 and to do away with variations that are allowed to the rules.

This is being done in advance of the introduction across Europe of digital tachometers, which will record coach journeys to make enforcing the rules easier.

Lack of sleep may well not be the cause of this accident.

Drivers tend to fall asleep on straight, monotonous motorways.

This coach was negotiating a sliproad, and it is possible the driver was lost, making it less likely he was sleepy.