Almost half of the UK's flagship cycling routes are unsafe for a child of 12 to use, a transport charity says.
Sustrans says poor surfaces, traffic, and too many barriers are making more than 7,500 miles of tracks inaccessible to young users, and other groups.
"There may as well be a 'no entry' sign on their local path," the group's chief executive Xavier Brice said.
The group is calling for an overhaul of the 16,575 miles of cycle routes "to make the network safer for everyone".
It says its long-term goal is to make the network traffic-free and "safe for a 12-year-old to use on their own".
A route being safe for a 12-year-old is a safety benchmark set by the UK government.
But according to Sustrans, two-thirds of the network is on the road - including nearly 2,000 miles of A and B roads.
The Paths for Everyone report, a review and independent audit of the network commissioned by Sustrans, classified 42% of the UK's Cycle Network as "very poor".
As well as being unsafe for children, it says thousands of miles of cycle routes are unsuitable for those with mobility issues and the less physically active.
The charity - which itself owns 500 miles of the network - says improvements could be made, including:
- doubling the number of paths away from cars, from 5,000 to 10,000 miles
- diverting all routes off busy and fast-moving roads onto quieter routes
- removing or redesigning 16,000 barriers, to improve accessibility
- improved safety at road and rail junctions
- introducing wider, better surfaced paths
It says these improvements would cost £2.8bn and would lead to the number of users rising from 4.4 million in 2017 to 8.4 million.
The review has highlighted 50 so-called "activation projects" which Sustrans aims to see completed by 2023, at a cost of £60 million. These include:
- rerouting the National Route 5 between Flint and Connah's Quay in North Wales to circumvent a major A road and create a new traffic-free path following the coastline
- bridging the River Bann in Northern Ireland to allow cyclists to complete the 113-mile Lap the Lough circuit, ending the current 16-mile detour
- realigning the National Route 76 in Stirling to avoid the multi-lane Manor Powis roundabout on the A907
Cycling and walking minister Jesse Norman said the cycle network was a great asset for cyclists and walkers but the report showed more needed to be done to make it fully accessible.
Earlier in the year, the government announced £1m to repair and upgrade sections of the routes.
The Scottish Government has committed £7m towards the development and maintenance of the paths in Scotland.