From wikipedia - 

Legislation

The use of compression release engine brakes may cause a vehicle to make a loud chattering or "machine gun" exhaust noise, especially vehicles having high flow mufflers, or no mufflers at all, causing many communities in the United States to prohibit compression braking within municipal limits. Drivers are notified by roadside signs with legends such as "Brake Retarders Prohibited," "Engine Braking Restricted," "Jake Brakes Prohibited," "No Jake Brakes," "Compression Braking Prohibited," or "Unmuffled Compression Braking Prohibited," and enforcement is typically through traffic fines. Such prohibitions have led to the development of new types of mufflers andturbochargers to better silence compression braking noise.

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NOTE:   Jacobs Brakes have not been banned, removed from engines, nor have they been outlawed.    Instead new types of mufflers have been developed to better silence the noise.