FCDC: Forecast-Conditioned Delay Correction for Traffic Forecasting

Traffic changes can be propagated between connected locations with a delay, so observations available at the forecasting origin may remain useful during the prediction interval. When these observations are used for correction, the already-predicted trajectory must be taken into account. In Forecast-Conditioned Delay Correction (FCDC), the complete multistep forecast is supplied directly to a compact signed readout, alongside local history and delayed evidence. The base forecast is formed by adding a global backbone prediction and a shared linear own-history prediction. Historical values are routed into an extended arrival window through learned edge-lag distributions; available lags are combined by a history-dependent gate, and messages are normalized over valid sources. All branches are trained jointly, without a cache of realized forecast errors. With local evidence fixed, correction signs can be reversed by changing the forecast input; such reversals are excluded by the corresponding unconditioned readout. FCDC and seven controlled variants are evaluated with five seeds on four PEMS datasets. FCDC's mean MAE is 0.62–2.29% lower than the best recorded external baseline on each dataset. Its average relative MAE reductions against variants without forecast input and without delay correction are 0.63% and 1.38%, respectively, with lower overall MAE in every matched-seed comparison.