gardun:
There’s currently a 50 limit on the M4 between 45 & 46. So now you need to drop another gear to get up the hill - more revs = more exhaust = more pollution. Not to mention noise.
They could have a chap sat behind a desk somewhere monitoring the sensors at road networks with inclines & change road speeds accordingly when pollution levels rise 
These new AQMesh air quality monitors which can be specified to monitor a single gas or up to 6 gases, as well as PM, noise and wind speed & direction all from a single unit. Measures gases NO, NO2, O3, CO, SO2, H2S and TVOC using the latest generation of electrochemical sensors.
CO2 monitoring with a NDIR sensor offering real-time localised air quality information and data analysis to the cloud.
Measures particulates PM1, PM2.5, PM10, TPC and TSP (up to 30 microns) with a light-scattering optical particle counter
Noise monitoring with an omnidirectional microphone & a meteorological sensor for wind speed and direction measurement.
