Vorpal wrote:I used to go fairly regularly to Colchester Zoo, and Cycle Travel pretty consistently makes different choices in that area than I would.
For example, from Silver End to Colchester Zoo, Cycle Travel puts me on Hollow Road to Kelvedon, then onto the A12 side path, then across the A12 to Easthorpe Road. The openings have been closed on the A12 in this area, but it would, in any case be a horrible, horrible crossing, especially if you had any younger cyclists with. The next crossing I am aware of on the A12 is at Easthorpe Green, abut I still wouldn't consider crossing there, even if I was alone.
A *much* better route is to take the B1023 Inworth Road to New Road, then go through Messing and take minor roads, which is far more pleasant than the A12 side path. One can then come out at Fountain Lane and have relatively short distance on a busy B road, or avoid more motor traffic a bit longer, cross the B road at Birch, take NCR 1, and turn off at a bridleway that goes (almost?) to the zoo.
This is actually quite a fun example...!
Like pretty much any route-planner, cycle.travel works by scoring each individual section of road and each turn, adding them up, and choosing the route with the best score. In the example you've given, the two routes (one via the A12 cycleway, the other via Messing) have almost exactly the same score
. The difference between the two is just 0.18% (5866 vs 5877, for what it's worth). It's not often that two alternatives are so closely tied.
I think my gut reaction would be to take the Messing route rather than the cycleway route, too. So the question is why c.t is (narrowly) choosing the other route, and there are two reasons that I can see. One is that it doesn't differentiate between a cycleway beside a busy road and a cycleway in the middle of nowhere, because they're both just marked as 'cycleway' in OSM. I'd very much like to de-emphasise this sort of cycleway beside a rural dual carriageway, because they're not generally a whole bunch of fun to ride; and in fact, doing this has been on my to-do list ever since starting the site. But it's a Hard Problem to solve. I return to the problem every few weeks, but I haven't yet found a way of detecting such cycleways that wouldn't take (literally) days of server power...
But the other reason is fixable, and that's to do with the penalty that c.t gives the A12 crossing. At present it knows that it's crossing a green-signed A road, and gives it a penalty accordingly. But such crossings can vary from this
, which I do all the time and which is very benign, to the example you've found.
I can get the crossing penalty to be higher for the busiest A roads. It will require a bit of jiggery-pokery but it should be doable. That will mean it's still happy to route across the A44 as in my example, but much more wary about crossing the A12. I'll have a play and post here when I've got something working.
Why use the A12 side path & crossing, and not use the A12 side path to Marks Tey, like Google suggests?
In that case it's because carrying on to Marks Tey means you have to follow the A120 for a bit (which has a high traffic count, so c.t will try and avoid it) and go across two roundabouts.