DDOT traffic calming policy: only two traffic calming measures permitted per street

Bloomingdale resident John Salatti mentions a policy by DDOT that a given street can only get two forms of traffic calming:

About 2007, Bryant Street NW received two forms of traffic calming, becoming one way and the installation of parking boxes. DDOT policy is not to add a third form. 

I was unaware of this DDOT policy, but I will assume that it is correct.