# Known Issues

#### 2020-11-04

This vignette highlights some known limitations or bugs with OpenTripPlanner as well as suggested solutions.

## Reasons for Routing to Fail

If you find OTP can not find a route here are some common reasons to check:

### Start or End is too far from the road network

OTP will snap fromPlace and toPlace coordinates to the road network, but only for a limited distance. If your points are far from the road network (e.g. in a lake or middle of a park) then OTP will fail to find a route.

### Mode Specific Limits

OTP does not support all mode combinations (e.g. walk + drive) so some places may only be accessible by certain modes. For example, you can’t walk on a motorway or drive on a path. Use the debug layers to check for mode restrictions.

### Maximum walk to transit

By default, OTP caps the maximum walking distance to a transit stop at a low level, so some areas are unreachable by transit. Increase the maximum walking distance to get better results.

### Driving on Roads with cycleway tag

A known bug that stops driving on any road with cycling infrastructure. https://groups.google.com/forum/#!topic/opentripplanner-users/BOv1J32k6Sc

## Speeding up routing

If you are doing a large amount of routing consider the following options.

1. Use multicore routing using ncores argument of otp_plan()
2. Reduce the area, for example, if you are only routing in one city you don’t need a whole country graph.
3. Remove unneeded roads using osmfilter or OSMtools for example if you are only interested in driving you can remove footpaths and cycleways. This will simplify your graph and provide a small performance boost.
4. Upgrading your computer, a new fast CPU with more cores will route faster.

## Elevation Data

It is common for GeoTIFF to have a no data value often the maximum possible value. OTP can misinterpret this as an elevation value. So set your no data values in your elevation data to something more plausible like 0.

Note that OTP does not support all types of GeoTIFF compression so you may have to change the compression type of the image if you are experiencing problems.