# Road-only pavement gain r313

The r311 L4RB capture still showed an underpass roadway that was too dark. A
same-camera comparison isolated a road-surface gain from the global city-light
gain. `CITY_ROAD_SURFACE_GAIN` multiplies rendered road-material RGB after the
existing texture, vertex-prelight, and nearby-light calculations. It does not
change city lighting or non-road batches. The value is available as the
`cityRoadGain` URL parameter for review; the packaged default is 1.6.

Chrome 150 loaded L4RB at the same start position in two packaged builds. The
road crop `(390,390)–(930,650)` changed from mean RGB `(16.5,17.1,17.6)` at
r311's gain 1.0 to `(26.4,27.4,28.1)` at gain 1.6. The nearby building crop
`(150,60)–(410,125)` remained `(23.0,29.3,20.3)`. A Route 450 L4RA capture
also retained readable yellow and white source markings with the road-only
gain. The 1.6 value is a viewer exposure correction selected by image
comparison; it is not a recovered retail lighting constant.

The r313 screenshot is `webgl-city/review/images/445-r313-road-only-gain.png`.
The underpass remains a night scene and the car remains pale/flat, so neither
lighting nor vehicle appearance is considered complete.