URBAN ROAD DESIGN Lecture 5 Alignment and Profile

URBAN ROAD DESIGN Lecture 5 - Alignment and Profile of Urban Road School of Civil Engineering 孙仁娟 2012. 3. 13

Basic Terms • The geometric design of highway deals with the positioning of the physical elements of the roadway according to standards and constraints. • The basic objective in geometric design is to provide a smooth-flowing, crash-free facility. • Geometric design can be broken into three main parts: horizontal alignment, vertical alignment (profile) and cross-section. Combined, they provide a threedimensional layout for a roadway.

Basic Terms • The alignment is the route of the road, defined as a series of horizontal tangents and curves. • The profile is the vertical aspect of the road, including crest and sag curves, and the straight grades connecting them. • The cross section shows the position and number of vehicle and bicycle lanes and sidewalks, along with their cross slope or bankng. Cross sections also show drainage features, pavement structure and other items outside the category of geometric design.

Standard & specification • Urban roads are designed in conjunction with design guidelines and standards. • The guidelines take into account speed, vehicle type, road grade (slope), view obstructions, and stopping distance. • They are listed in 《城市道路 程技术标准》(CJJ -2009) 《城市道路设计规范》（CJJ 37 -90)

Horizontal alignment-- • Horizontal alignment in urban road design consists of straight sections of road, known as tangents, connected by horizontal curves. • The design of a horizontal curve entails the determination of a minimum radius (based on speed limit), curve length, and objects obstructing the view of the driver. • If there is an object obstructing the view around a corner or curve, the engineer must work to ensure that drivers can see far enough to stop to avoid an accident or accelerate to join traffic.

Terminology • • R = Radius PC = Point of Curvature (point at which the curve begins) PT = Point of Tangent (point at which the curve ends) PI = Point of Intersection (point at which the two tangents intersect) T = Tangent Length C = Long Chord Length (straight line between PC and PT) L = Curve Length M = Middle Ordinate, now known as HSO - Horizontal Sightline Offset (distance from sight-obstructing object to the middle of the outside lane) • e = Rate of Superelevation • f = Coefficient of Side Friction • u = Vehicle Speed

Horizontal alignment-- • • Straight line Horizontal and circular curve Transition curve Sight distance

Straight line • Highway • Urban road

Horizontal and circular curve • Minimum radius: • Highway • Urban road

Horizontal and circular curve • General minimum radius? • Ultimate minimum radius? • Minimum radius without superelevation?

Horizontal and circular curve • Forces on banked roadways

Horizontal and circular curve • General minimum radius? • Ultimate minimum radius? • Minimum radius without superelevation?

Horizontal and circular curve • Radius of curvature • Equilibrium of forces : sideway force coefficient : superelevation

Horizontal and circular curve • Practical limits on superelevation – Climate – Constructability – Adjacent land use • Side friction factor variations – Vehicle speed – Pavement texture – Tire condition

Horizontal and circular curve

Horizontal and circular curve • Highway

Horizontal and circular curve • Urban road • Dry condition: 0. 4～ 0. 8， • Wet asphalt: 0. 25～ 0. 40， • Ice condition: less than 0. 2

Horizontal and circular curve • Urban road

Transition curve/easement curve

Transition curve/easement curve from the 2001 Caltrans Highway Design Manual

Transition curve/easement curve

Transition curve/easement curve No Spiral from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

Sight distance • Sight distance (视距） is how far a road user (usually a vehicle driver) can see before the line of sight is blocked by a hill crest, or an obstacle on the inside of a horizontal curve or intersection. • Stopping sight distance （停车视距）is the distance traveled while the vehicle driver perceives a situation requiring a stop, realizes that stopping is necessary, applies the brake, and comes to a stop.

Sight distance • Stopping sight distance（停车视距） S停=S 1+S 2+ （m） • 会车视距 （m）

Sight distance Passing sight distance • 全超车视距： • 最小超车视距

Sight distance • Highway

Sight distance • Urban road

Profile • • • The profile of a road consists of road slopes, called grades, connected by vertical curves. Vertical curves are used to provide a gradual change from one road slope to another, so that vehicles may smoothly navigate grade changes as they travel. Sag vertical curves are those that have a tangent slope at the end of the curve that is higher than that of the beginning of the curve. When driving on a road, a sag curve would appear as a valley, with the vehicle first going downhill before reaching the bottom of the curve and continuing uphill or level. Crest vertical curves are those that have a tangent slope at the end of the curve that is lower than that of the beginning of the curve. When driving on a crest curve, the road appears as a hill, with the vehicle first going uphill before reaching the top of the curve and continuing downhill.

Terminology • A = absolute value of the difference in grades (initial minus final, expressed in percent) • BVC = begin of vertical curve • EVT = end of vertical tangent • G 1 = initial roadway (tangent)slope • G 2 = final roadway (tangent)slope • = Height of eye above roadway, measured in meters or feet • = Height of object above roadway, measured in meters or feet • L = curve length (along the x-axis) • PVI = point of vertical interception (intersection of initial and final grades) • tangent elevation = elevation of a point along the initial tangent • x = distance from PTC/BVC • Y (offset) = vertical distance from the initial tangent to the curve • Y’ = curve elevation = tangent elevation - offset

Profile • Objective: – Determine elevation to ensure • Proper drainage • Acceptable level of safety • Primary challenge – Transition between two grades – Vertical curves G 1 G 2 Crest Vertical Curve G 1 Sag Vertical Curve G 2

Crest Vertical Curves SSD PVI Line of Sight PVC G 1 PVT h 2 h 1 L G 2

Sag Vertical Curves Light Beam Distance (SSD) G 1 headlight beam (diverging from LOS by β degrees) PVT PVC h 1 G 2 PVI L h 2=0

Profile • Vertical grade and length of vertical slope • Radius and length of vertical curve

Vertical grade and length of vertical slope • Highway • Urban road • 表 6. 3. 2 最大纵坡 100 80 60 50 40 30 20 最大纵坡推荐值 (%) 3 4 5 5. 5 6 7 8 最大纵坡限制值 (%) 4 5 设计速度（km/h) 6 8 9

Vertical grade and length of vertical slope

Vertical grade and length of vertical slope • Highway • Urban road

Vertical grade and length of vertical slope Minimum length of the vertical slope 1. Restraint the centrifugal force (限制离心力） 一般情况下，单位车重的离心力（F/G）控制在 0. 020～ 0. 03之间， 则最小竖曲线长度 为： 2. Restraint the running time （限制行程时间过程） 3. Meet the requirement of sight distance (满足视距要求 ) 返回 上一页 下一页 退出

Radius and length of vertical curve • Highway

Radius and length of vertical curve • Urban road

Design of horizontal and vertical alignment • Match of horizontal and vertical curve • Design procedures of alignment-horizontal • Design procedures of alignment-vertical

Match of horizontal and vertical curve • Urban road

Questions?