OPTIMAL DRIVING STRATEGIES FOR A TRAIN JOURNEY WITH SPEED LIMITS

How should a vehicle be driven to minimise fuel consumption? In this p aper we consider the case where a train is to be driven along a straig ht, level track, but where speed limits may apply over parts of the tr ack. The journey is to be completed within a specified time using as l ittle fuel as possible. For a journey without speed limits, the optima l driving strategy typically requires full power, speed holding, coast ing and full braking, in that order. The holding speed and braking spe ed can be determined from the vehicle characteristics and the time ava ilable to complete the journey. If the vehicle has discrete control se ttings, the holding phase should be approximated by alternate coast an d power phases between two critical speeds. For a journey with speed l imits, a similar strategy applies. For each given journey time there i s a unique holding speed. On intervals of track where the speed limit is below the desired holding speed, the speed must be held at the limi t. If braking is necessary on an interval, the speed at which braking commences is determined in part by the holding speed for the interval. For vehicles with discrete control, speed-holding is approximated by alternate coast and power phases between two critical speeds, or betwe en a lower critical speed and the speed limit.