open google maps to bus directions

I realise that you can open the google maps app ready for directions by doing something like this:

NSString* urlString = @"http://maps.google.com/maps?saddr=London+UK&daddr=Birmingham+UK";
[[UIApplication sharedApplication] openURL:[NSURL URLWithString: urlString]];

But is there a parameter I can add to automatically switch to bus directions? Apple's developer document doesn't seem to mention anything about it:

https://developer.apple.com/library/archive/featuredarticles/iPhoneURLScheme_Reference/MapLinks/MapLinks.html