14.2 Hinge Points, Catch Points, and Grade Breaks

14.2 Hinge Points, Catch Points, and Grade Breaks

Quick Answer: From CL you walk the template: traveled way, grade break at ETW, shoulder, hinge (HP) at ES, then the cut or fill slope to the catch (CP / daylight) on original ground. Level-ground catch offset from the hinge = depth × slope ratio. 6.00 ft of fill on 2:1 is 12.00 ft of horizontal. On the worked two-lane typical, hinges sit at 18.00 ft and both catches sit at 30.00 ft from CL.

Item B of Domain V is locating and setting those critical cross-section points. You read them from the typical section plus the original-ground (OG) shot, not from a contour sketch alone. Contours and earthwork volumes are Chapter 12; here the job is where the lath goes.

The Typical Roadway Section

Look upstation. Offsets increase right and left of centerline (CL). Profile grade (PG) is often at CL of the traveled way on a crowned tangent.

A grade break is a change in slope on the design surface: the crown (2% down both ways from CL), the shoulder break (lane 2% to shoulder 4%), a match line (ML), or the hinge itself (shoulder to 2:1). The catch is not a template slope change. It is where the last design slope hits the ground that is already there.

Hinge vs catch, one sentence each. The hinge is on the design. The catch is on the ground. Moving the hinge (wider shoulder, added gutter) moves the catch even if the slope ratio is unchanged.

On a curbed street the hinge may sit at TBC, at the back of sidewalk, or at a specified daylight line behind the walk. All curbs are staked to the flow line in Caltrans practice: FL is the lowest point of the curb’s top surface in a standard (non-superelevated) orientation, or the pavement-to-face intersection when there is no gutter. A 6-inch curb face is 0.50 ft from FL up to TC.

Slope Ratio and the Level-Ground Catch

Side slopes are horizontal:vertical. 2:1 means 2 ft horizontal for 1 ft vertical (a 50% slope). 1.5:1 is steeper; 4:1 is flatter. Caltrans marks the ratio without a plus or minus; cut versus fill is in the C or F and in which way the slope runs from the hinge.

Fill drops from the hinge to catch. Cut rises from the hinge to catch (or drops from catch down to the hinge — same slope).

Level-ground formula (OG flat through the hinge and catch):

offset from hinge to catch = depth × (horizontal / vertical)

2:1 fill, 6.00 ft fill → 6.00 × 2 = 12.00 ft horizontal from the hinge to the catch.

That formula is exact only when OG is level. If OG slopes, the catch moves (Section 14.3). CES stems that give a single depth and a ratio, and that never give a ground slope, want this product.

Worked Full Typical Section (Cut and Fill Sides)

Sta 18+50. Two-lane rural section, PG at CL = 412.40 ft.

• 12.00 ft lanes, 2.0% down from CL
• 6.00 ft shoulders, 4.0% down from ETW
• 2:1 fill right, 2:1 cut left
• Treat OG as locally level at each hinge for this first pass

Lane drop = 12.00 × 0.020 = 0.24 ft
ETW elevation = 412.40 − 0.24 = 412.16 ft at 12.00 ft offset (grade break: 2% → 4%).

Shoulder drop = 6.00 × 0.040 = 0.24 ft
Hinge (ES) elevation = 412.16 − 0.24 = 411.92 ft at 18.00 ft LT and RT.

Right — fill. OG at the right hinge = 405.92 ft.
Fill depth = 411.92 − 405.92 = 6.00 ft.
Catch from hinge = 6.00 × 2 = 12.00 ft.
Catch = 18.00 + 12.00 = 30.00 ft RT, elevation 405.92 ft.

Left — cut. OG at the left hinge = 417.92 ft.
Cut depth = 417.92 − 411.92 = 6.00 ft.
Catch from hinge = 12.00 ft.
Catch = 30.00 ft LT, elevation 417.92 ft.

Curb / flowline variant at the same CL grade: drop the 12-ft lane at 2% to a gutter flow line at 12.00 ft RT. FL = 412.16 ft. A 6-inch curb face puts TC = 412.16 + 0.50 = 412.66 ft. If the typical then uses a 2-ft sidewalk at 2% behind TBC, that sidewalk is another grade break; the hinge for the cut slope is at the back of walk, not at FL. Do not hang a 2:1 catch off the flow line unless the typical shows the side slope starting there.

Offsets You Must Not Mix

Offset from CL to hinge is geometry of the paved template (lanes + shoulders, plus sidewalk, ditch, or bench if shown). Offset from hinge to catch is earthwork. Adding them gives offset from CL to catch — the number the slope-stake crew occupies first.

Traps: (1) 6 × 2 = 12 reported as the offset from CL, forgetting the 18.00 ft of pavement/shoulder; (2) using 2% as if it were 2:1; (3) putting the hinge at ETW when the typical shows a shoulder; (4) calling the catch a hinge because both are “the edge of the dirt”; (5) applying the level-ground product on a sidehill where OG has slope — the catch is then not 12 ft from a 6-ft hinge depth (Section 14.3).

On Caltrans point-to-point slope-stake cards, each C/F + distance + ratio after the catch describes the next design segment from the previous slope point, not from CL. The 12.00 ft on 2:1 from catch to hinge is that segment. The 18.00 ft from hinge to CL is a different pair (often with the shoulder and lane slopes, not 2:1).

If a bench sits in a cut (Caltrans example language: cut on 1:1 to a bench toe, then a flat 10:1 lip, then another 1:1 to the hinge), every bench lip is a grade break and a staking point. Catch is still only the OG intersection.