Speech Recognition Project - HMM
I learnt to use HTK based on this very basic tutorial

http://www.info2.uqam.ca/~boukadoum_m/DIC9315/Notes/Markov/HTK_basic_tutorial.pdf

It details how to make a yes/no recogniser. It should get you off to a good start at least.  There is also some HTK code on the main HTK site that allows you to perform real time speech recognition.

To improve robustness, you might also consider training the recogniser on speech tokens that are mixed with the kind of noises that you'd expect to hear around your receiver. You could place a recording device near to the traffic light and record a day's worth of background material, then randomly select samples windows to add to your speech corpus at various levels.