However the remaining single line sections proved a serious delaying factor for the traffic. Safety on single line sections was secured by every train carrying a token for each single line; instruments at the signal boxes were electrically interlocked to ensure that only one token could be out of the instruments for any one section at a time. The tokens had to be handed to the driver of every train by the signalman, and in the case of express trains, this meant slowing to walking pace to secure the handover.