You really have to read this aloud to get the punchline..

There's two pieces of tarmac sitting at a bar. One say's "I'm from the M1 and have 50,000 cars rolling over me each day and I'm really hard". The other says, "that's nothing, I'm from the M25 and have 500,000 cars a day rolling over me".

"Christ!" says the first tarmac, "you are hard".

Just then, a red piece of tarmac walks in. The M25 tarmac runs off and hides under a table. "What you doing under there?" says the M1 tarmac, "I thought you were hard?"

"I am" he says, "but that guy over there's a cycle path!"
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Delete! Delete!