Consider commuter trains serving contiguous stations. At each station, trains stop to load and unload passengers and this requires a fixed "dwell" time, d. Between stations, trains travel at cruise speed, v. We ignore the effects of acceleration and deceleration. For safety reasons, consecutive trains must always be physically separated by a minimum block distance, b, where block distance is measured from the rear end of a leading train to the front end of the following train. Trains have physical length L. Determine the maximum flow of trains possible given the above operating conditions. Express this maximum flow in terms of the variables given.