Intersection Design, Traffic Islands, Sight Distance, and Railroad Crossings

Vocabulary practice flashcards covering intersection types, geometric configurations, traffic islands, pavement widths, intersection sight distance cases, and railroad grade crossing designs.

Intersection

An area shared by two or more roads whose primary function is to facilitate the change of route directions.

Grade-Separated Intersection Without Ramps

An intersection consisting of structures that allow intersecting streams of traffic to cross at different vertical levels without interruption, with no connecting provisions between the roads.

Interchange

A grade-separated intersection with ramps that allow traffic to move from one intersecting road to another across different vertical levels.

At-Grade Intersection

A road junction where intersecting roads meet at the same level without vertical separation, creating direct conflict points between crossing traffic streams.

Trumpet Interchange

A three-way, grade-separated road junction where one highway terminates into another using a combination of direct and looped ramps resembling the bell of a musical trumpet.

Three-Leg Directional Interchange

A high-capacity road junction where all turning movements between three intersecting highway legs are handled by sweeping flyovers or underpasses that permit full highway speeds.

One Quadrant Interchange

A three- or four-leg road junction where all connecting ramps are consolidated into a single quadrant of the intersection.

Diamond Interchange

A cost-effective road junction where a high-speed highway crosses a minor surface road via four diagonal one-way ramps that resemble a diamond shape from an aerial view.

Single-Point Urban Interchange (SPUI)

A modification of the diamond interchange where all four ramp terminals converge at a single, centralized traffic signal located directly over or under the freeway.

Partial Cloverleaf Interchange (Parclo)

A four-leg road junction combining elements of a standard diamond interchange with one to three loop ramps of a full cloverleaf.

Full Cloverleaf Interchange

A four-way, grade-separated junction featuring four circular loop ramps (one in each quadrant) allowing all turning movements between two crossing highways without traffic signals or stop signs.

All-Directional Four-Leg Interchange (Stack Interchange)

A multi-level system interchange (often four levels) where all turning movements are served by direct, high-speed directional flyovers.

Plain 'T' Intersection

A three-way at-grade road junction where one street ends at a continuous crossroad without physical traffic islands, medians, or painted turn lanes.

'T' Intersection with a Right-Turn Lane

A three-way junction where the continuous through-road features an auxiliary right-turn lane dedicated to vehicles decelerating to exit onto the terminating road.

'T' Intersection with a Right-Hand Passing Lane

A bypass-T intersection where an extra bypass lane is provided on the right side of the continuous through-road opposite the terminating street to allow through vehicles to pass decelerating left-turning vehicles.

'T' Intersection with a Divisional Island and Turning Roadways

A channelized three-way junction incorporating a physical median barrier on the terminating road along with dedicated, curved slip lanes for turning traffic.

Channelized T-Intersection

A design that converts a two-lane road into a divided highway through an intersection, incorporating a left-turn storage lane, right-turn lane, and acceleration lane.

Rotary

A large-diameter traffic circle (typically greater than $90\,\text{m}$) that accommodates operating speeds exceeding $48\,\text{km/h}$ with minimal horizontal deflection for through traffic.

Neighborhood Traffic Circle

A small circular intersection used on local residential streets for traffic calming and aesthetics, operating at low speeds with yield, stop, or uncontrolled approaches.

Modern Roundabout

A circular intersection characterized by mandatory yield control for entering vehicles, geometric deflection to keep speeds under $48\,\text{km/h}$, and no parking within the circulatory roadway.

Mountable Curb

A concrete curb constructed with a sloped face of $45^\circ$ or less that vehicles can cross when necessary without sustaining significant damage.

Barrier Curb

A steep curb constructed with a nearly vertical face designed to prevent vehicles from encroaching onto islands or leaving the designated traveled way.

Flush Island

A traffic island formed flush with the road pavement using paint, thermoplastic striping, or raised retroreflective markers.

Channelized Island

A traffic island designed to direct vehicles into specific paths and eliminate driver confusion by converting excess intersection pavement into designated channels.

Divisional Island

A traffic island placed on an undivided roadway to alert drivers of an approaching intersection, divide opposing or same-direction traffic streams, and guide turning paths.

Refuge Island

A pedestrian island located at wide urban intersections to provide a protected waiting area for pedestrians and wheelchairs, or for loading/unloading transit passengers.

Case I Turning Roadway Operation

A one-lane, one-way turning roadway design without provision for passing a stalled vehicle, governed by the width equation $W = U + C + Z$ .

Case II Turning Roadway Operation

A one-lane, one-way turning roadway design with provision for passing a stalled vehicle, governed by the width equation $W = U_1 + U_2 + 2C + F_A + F_B$.

Case III Turning Roadway Operation

A two-lane turning roadway design (either one-way or two-way), governed by the width equation $W = U_1 + U_2 + 2C + F_A + F_B + Z$ .

Extra Width Allowance ($Z$)

An additional width factor to compensate for difficulty of steering and driving on curves, calculated as $Z = \frac{v}{\sqrt{R}}$, where $v$ is design speed in $\text{km/h}$ and $R$ is curve radius in meters.

Vehicle Track Width on Curve ($U$)

The swept path width of a vehicle on a curve, calculated by $U = u + R - \sqrt{R^2 - \sum L_i^2}$, where $u$ is track width on tangent, $R$ is turning radius, and $L_i$ is the wheelbase between consecutive axles.

Sight Triangle

An unobstructed triangular area formed by the line of sight between drivers approaching an intersection and the paths of conflicting vehicles.

Approach Sight Triangle

A sight triangle that provides sufficient sight distance for drivers approaching an uncontrolled or yield-controlled intersection to slow down or stop before a potential collision point.

Departure Sight Triangle

A sight triangle that allows the driver of a vehicle stopped on a minor road to view approaching traffic and safely enter or cross the major road.

Case A Intersection Sight Distance

The sight distance requirement for no-control intersections, permitting drivers approaching on cross streets to detect each other and adjust speed to avoid collisions.

Case B1 Intersection Sight Distance

The sight distance requirement for a stopped vehicle on a minor road making a left turn into a major highway, clearing approaching traffic from the left and joining traffic from the right.

Case B2 Intersection Sight Distance

The sight distance requirement for a stopped vehicle on a minor road turning right onto a major highway or making a right turn on red.

Case B3 Intersection Sight Distance

The sight distance requirement for a stopped vehicle on a minor road crossing all lanes of a major highway.

Case C Intersection Sight Distance

The sight distance requirements for yield-controlled minor-road approaches, covering crossing maneuvers (Case C1) and left or right turning maneuvers (Case C2).

Case D Intersection Sight Distance

Sight distance requirements at signalized intersections ensuring drivers of first-stopped vehicles on all approaches see one another and left turners have adequate gap visibility.

Case E Intersection Sight Distance

The sight distance requirement for all-way stop-controlled intersections, requiring only that the first stopped vehicle on each approach be visible to drivers stopped on all other approaches.

Case F Intersection Sight Distance

The sight distance required for a vehicle on a major highway to safely execute a left turn across opposing traffic lanes.

Skewed Intersection Sight Distance

The design condition where roads intersect at an angle other than $90^\circ$, requiring the crossing distance to be calculated as the major road width divided by $\sin(\theta)$.

Railroad Grade Crossing Sight Triangle

A clear sight area defined by legs along the highway approach ($d_H$) and along the railroad track ($d_T$) that allows drivers to stop before the tracks or safely clear the crossing before a train arrives.