Traffic impact analysis (TIA) leverages both conventional and Urban SDK location data to estimate number of trips generated from a new development project. The process consists of multiple steps which are detailed below.
Steps of TIA
Development and Influence Area Selection
The feature is developed by leveraging the geohash technology that has been leveraged in other Urban SDK projects. The size of the influence area (a.k.a. impact area) is determined by number of neighboring geohashes that surround the central geohash(es) where the new development will be built. Once the user draws an approximate shape of the new development polygon, the landing geohash and its neighboring geohashes are identified.
Trip Generation Estimation
ITE trip generation manual procedure is used to calculate the number of trips generated by a given development code and characteristics as the user enters appropriate information. For example, let us say a hospital is set to be built on a parcel. Upon the appropriate land use (here, hospital) selection and entering the number of units, time period and Urban setting by the user, number of trips generated by the residential complex is calculated for retrieving the relevant information from ITE trip generation manual. For example, the following snapshot from the manual:
indicates on average, there will be 22.32 weekday trips/bed if a hospital is built in a general urban/suburban setting. Therefore, if the project has 200 beds, the number of trips generated will be:
200 x 22.32 = 4,464 weekday trips
Trip Distribution Module
The estimated trips are distributed to the geohashes of the influence area based on percentages that are obtained from Urban SDK origin-destination (OD) products. Urban SDK location-based data have used to obtain geohash level OD data. The distribution percentages from OD data are used to determine the number of trips ending in each neighboring geohash. The figure below for example, shows how 4,464 trips end in neighboring geohashes,
New dev. geohash
Current Condition, Future Condition and Background traffic
The steps explained above, estimate and distribute net number of trips for a given development type. TIA has the capability of incorporating background traffic and estimating current and future condition if appropriate data is presented to it. In particular, background traffic, traffic growth factor from a pre-established travel demand model can be processed (to make suitable for TIA) and included in TIA enabling it to estimate total number of trips (rather net number of trips from development) from the development geohashes to its neighbors. Similarly, by inclusion of growth factor, future number of trips and their distribution can be estimated for a projected year.
Many assumptions have been made in the process of estimation the traffic impacts of new developments. These assumptions are not necessarily related to TIA tool but more rooted in the methodology of trips and estimation in area of transportation engineering. The readers are encouraged to refer to ITE trip generation manual and documentation for more details on the methodologies and their underlying assumptions. For example, average number of trips for each land use code is estimated using linear regression. Therefore, all linear regression assumptions hold. Turning to assumption made related to TIA tool, since the minimum level of analysis is geohash rather than parcel, the location of the development within its geohash does not change the number of trips and the way they are distributed. Of course, if a development is overlapped by more than one geohash, the user gets to choose the most appropriate development geohash. However, after the selection, the selected geohash will be used to run the calculated and distribution. In terms of background traffic and modeling current and future traffic, all travel demand modeling assumptions also apply.