Pedestrian campaigners Living Streets said research had found that not everyone met the official “assumed walking speed” used to set crossing times, which has not changed since the 1950s despite an ageing population.
The green man is normally on for four seconds, then flashes for a further six seconds before traffic lights turn green.
Living Streets spokeswoman Phillipa Hunt said: “As this independent research has found, the Department for Transport’s current assumed walking speed of 1.2 metres/second is too fast for many older people to manage, not to mention small children, parents with buggies or people with sight or mobility problems.
“We know that not having enough time to cross the road makes people feel rushed or harassed at best, and at worst creates impassable barriers to shops, services, family and friends.
“Just three seconds can make the difference between an older person feeling confident they can walk out of their front door, and feeling vulnerable and afraid to cross the road, in turn causing them to feel isolated.”
She said the research, by TRL, showed around one in five older people felt hurried or harassed when crossing a road.