State Highway Network Postmiles

The LRSN_Postmile feature class is an Esri Roads and Highways Network (or more generically a Linear Referencing Method) that represents the California State Highway System (Interstates, US Highways and State Highways) using the Caltrans Postmile System. The Caltrans Postmile System is fairly complex, where postmiles reset to 0.0 at county boundaries, temporality is managed through Postmile Prefixes and "Independent Alignments" (where right and left sides diverge around various obstacles and are postmiled differently) are managed with Postmile Suffixes. To accommodate this system, entire "Signed Routes" (e.g. 800+ miles of Interstate 5) are divided into a number of "Postmile Routes", where the Postmile Prefix and Postmile Suffix are managed as part of the Route ID, leaving just the numeric portion of the Postmile as the Postmile Route Measure. Additionally, while the Caltrans Postmile System is considered a "Centerline" system (with the exception of the aforementioned independent alignments), the LRSN_Postmile Network stores complete right and left "Carriageways" (the R/L carriageway designation is also part of the Route ID). The reason for this is to best support independent alignments AND to meet Federal Highway Administration requirements for every state's Linear Referencing System. To accommodate division of entire signed routes into multiple Postmile Routes, LRSN_Postmile is configured as a Roads and Highways "Line Feature", where every individual Postmile Route that comprises a Signed Route is tagged with a "Line ID" common to the Signed Route. This supports the ability to perform Dynamic Segmentation of linear events that begin on one Postmile Route and end on another, and the ability to automatically derive the Odometer Network directly from the Postmile Network. The Postmile Network is one of three Roads and Highways Networks maintained in Roads and Highways by Caltrans. The other two are the Odometer Network (also State Highway System only, and derived from the Postmile Network) and the AllRoads Network, which represents all public roads in California (not just state highways).LRSN_Postmile要素类（feature class）是Esri道路与高速公路网络（Esri Roads and Highways Network，亦可泛称为线性参考方法（Linear Referencing Method）），用于借助加州交通局（Caltrans）里程桩系统（Caltrans Postmile System）表征加利福尼亚州州级公路系统（含州际公路、美国国道及州道）。加州交通局里程桩系统结构较为复杂：里程桩会在县界处重置为0.0，临时性规则通过里程桩前缀（Postmile Prefixes）进行管理；而“独立线形（Independent Alignments）”——即左右两侧因各类障碍物分岔并采用不同里程桩编号的路段——则通过里程桩后缀（Postmile Suffixes）进行管理。为适配该系统，完整的“已签署路线（Signed Routes，例如全长800余英里的5号州际公路）”会被划分为多个“里程桩路线（Postmile Routes）”，其中里程桩前缀与后缀作为路线ID（Route ID）的组成部分进行管理，仅保留里程桩的数值部分作为里程桩路线度量值（Postmile Route Measure）。此外，尽管加州交通局里程桩系统被定义为“中心线”系统（前述独立线形路段除外），但LRSN_Postmile网络会存储完整的左右行车道（Carriageways），行车道的左右标识同样作为路线ID的一部分。该设计的初衷在于，一方面更好地支持独立线形路段，另一方面满足美国联邦公路管理局（Federal Highway Administration）对各州线性参考系统的规范要求。为实现已签署路线划分为多个里程桩路线的需求，LRSN_Postmile被配置为道路与高速公路类别的“线要素（Line Feature）”，构成某一已签署路线的所有独立里程桩路线，均会被标记为与该已签署路线共用的“线ID（Line ID）”。这一配置可支持对跨里程桩路线的线性事件进行动态分段（Dynamic Segmentation），同时支持直接从里程桩网络推导得到里程网络（Odometer Network）。该里程桩网络是加州交通局在道路与高速公路系统中维护的三类道路与高速公路网络之一，另外两类分别为里程网络（仅覆盖州级公路系统，由里程桩网络推导而来）以及全道路网络（AllRoads Network），后者涵盖加利福尼亚州内所有公共道路（而非仅州级公路）。