Related Clues:

• Slower to progress, maybe reading new word in classic
• They hold traveller up - American gun is effective in securing article
• Highway deeds holding up travellers
• Training's a possible cause of congestion
• Pieces by strolling players resurfacing, maybe?
• M25, say, has mechanism for carriageway repairs
• Jam makers?
• Way factory gives reason for stop-go procedure
• Maintenance operations that obstruct traffic
• Warning sign that's self-evidently untrue?