Original: Prototype Kingsway trolleybus no. 1379 , with exits on both sides with folding doors , was constructed for feasibility tests through the subway , but these were unsuccessful as trolleybuses would have had to run on battery power through the subway , headroom restrictions making it impossible to use overhead current collection .
Simplified: This was because the trolleybuses would have had to run on battery power through the subway . They would have had to have used battery power because headroom restrictions made it impossible to use overhead current collection .