In the Curious Incident of the Dog in the Night-time, how does Christopher deal with his behavioral problems on his way to London?

He really follows a lot of routine as best he can, and he concentrates on very practical steps he can take to avoid having behavioral problems. He is aware of how he tends to react, so he tried to be proactive to avoid those issue when possible.

For example, in Ch. 191 he becomes overwhelmed with the number of signs around him. Where this might normally cause him to shut down and start screaming or...

He really follows a lot of routine as best he can, and he concentrates on very practical steps he can take to avoid having behavioral problems. He is aware of how he tends to react, so he tried to be proactive to avoid those issue when possible.

For example, in Ch. 191 he becomes overwhelmed with the number of signs around him. Where this might normally cause him to shut down and start screaming or covering his ears and eyes, in this instance he focuses on something very practical:

"I pictured in my head a big red line across the floor which started at my feet and went through the tunnel and I started walking along the red line, saying 'left, right, left, right, left, right,' because sometimes when I am frightened or angry it helps to do something that has a rhythm to it like music or drumming, which is something Siobhan taught me to do" (Haddon).

Later, in Ch.197, he recognizes he is beginning to get very uncomfortable with the number of people on the train. In the past, he might have jumped out of the train, like he mentions he tried once to jump out of a moving car. However, he recognizes he is upset, and instead he "stood very still in the train carriage and didn't move" (Haddon).

Although he is not able to avoid ALL behavioral issues on the way to London, he does a pretty good job of avoiding several of them simply because he is very self-aware and proactive about preventing them.