The Highway-Runoff Database (HRDB) was developed by the U.S. Geological Survey (USGS), in cooperation with the Federal Highway Administration (FHWA) Office of Project Delivery and Environmental Review to provide planning-level information for decision makers, planners, and highway engineers to assess and mitigate possible adverse effects of highway runoff on the Nation's receiving waters (Granato and Cazenas, 2009; Granato, 2013; 2019; Granato and others, 2018; Granato and Friesz, 2021). The HRDB was assembled by using a Microsoft Access database application to facilitate use of the data and to calculate runoff-quality statistics with methods that properly handle censored-concentration data. The HRDB was first published as version 1.0 in cooperation with the FHWA in 2009 (Granato and Cazenas, 2009). The second version (1.0.0a) was published in cooperation with the Massachusetts Department of Transportation Highway Division to include data from Ohio and Massachusetts (Smith and Granato, 2010). The third version (1.0.0b) was published in cooperation with FHWA to include a substantial amount of additional data (Granato and others, 2018; Granato and Jones, 2019). The fourth version (1.1.0) was updated with additional data and modified to provide data-quality information within the Graphical User Interface (GUI), calculate statistics for multiple sites in batch mode, and output additional statistics. The fifth version (1.1.0a) was published in cooperation with the California Department of Transportation to add highway-runoff data collected in California. The sixth version published in this release (1.2.0) has been updated to include additional data, correct data-transfer errors in previous versions, add new parameter information, and modify the statistical output. This version includes data from 270 highway sites across the country (26 states); data from 8,108 storm events; and 119,224 concentration values with data for 418 different water-quality constituents or parameters.