***maintain***: i.e., stay within (the limits)   

>[TFD][1]: **3**.  to keep in a specified state, position, etc.  
>[ODO][2]: keep (something) at the same level or rate  

When you have not exceeded, i.e., stayed within the speed limit,  
>You maintained the speed limit.

Use case:
>[dailyindependentnig][3]: FRSC urges motorists to maintain speed limits  
[Miller et al. *Community Policing*][4]: ... maintain speed limit  
[Wild Trail in Bengal][5]: maintain speed limit of 20 kmph.  


  [1]: http://www.thefreedictionary.com/maintain
  [2]: http://www.oxforddictionaries.com/definition/english/maintain
  [3]: http://dailyindependentnig.com/2012/09/frsc-urges-motorists-to-maintain-speed-limits/
  [4]: http://books.google.co.in/books?id=SvFZVPas-mYC&pg=PA191&dq=%22maintain%20speed%20limit%22&hl=en&sa=X&ei=UqqpUqiQAsWOrQfwuoDwCw&redir_esc=y#v=onepage&q=%22maintain%20speed%20limit%22&f=false
  [5]: http://books.google.co.in/books?id=s2z6kVzswZ4C&pg=PT6&dq=%22maintain%20speed%20limit%22&hl=en&sa=X&ei=UqqpUqiQAsWOrQfwuoDwCw&redir_esc=y#v=onepage&q=%22maintain%20speed%20limit%22&f=false