The only drawing programme we have found to our knowledge that runs on Macs.

Quote from their website

RailModeller Pro is a planning tool for designing model railroad and slot car layouts.

Key features include:

- Layouts of up to 10 x 10km (6.2 x 6.2 miles) in size,

- More than 250 multi-brand libraries with 6000+ tracks and accessories

There is a free trial version available