A peek at a 1931 road map of Connecticut can be a disorienting experience. The cities and towns (except for Deep River) are the same as today; and you'll recognize a handful of highways, namely US 1, 5, 6, and 7, and state routes 8, 10, 12, and 32. But Route 10 is in the wrong place. US 7 veers off into New York. And no route other than the first eight looks familiar at all.

Connecticut's original highway system evolved over the course of eight years. Then, on Jan. 1, 1932, it was scrapped, and replaced with a new system that grew into the one we use today. I call this the "Great Renumbering", but that's not an official term. I tend to use the term "1920s" in this context to refer to the span starting with the first route numbers in 1923 and ending with the Great Renumbering in 1932.

When a year-old map is obsolete: Before and After the Great Renumbering
Scans from Socony New England Road Map, 1931 and 1932Left: South Central Connecticut, 1931.
Right: same area, 1932.
Both are scanned from the Socony Road Map of New England. (The black numerals are route numbers; the red ones alongside major roads are mileages.) Only US routes and a few New England Interstate routes survived the changeover.

History

In 1916, the state started marking routes with a system of colored bands on poles. East-west routes had red bands, north-south were blue, and diagonal or secondary routes were yellow. As more roads were built, however, this system became less effective; motorists needed a better way to identify routes.

Highway commissioners, hotel associations and members of the Automobile Club of America worked on a solution, culminating in an early April 1922 conference in New York announcing a proposed uniform numbering system for the entire United States.

New England and New York adopted the system. Other states such as Wisconsin (the pioneer in this respect) had also starting numbering their highways. The idea caught on so quickly that the New England Interstate system was short-lived: in 1926, a nationwide system of U.S. routes supplanted it. Many New England Interstate routes (such as NE 2) became US routes (such as US 5).

Numbering System

The New England Interstate route numbers were adopted in 1922; Connecticut added its state highway routes in 1923. From that point up to the 1932 renumbering, this convention, based on the New England Interstate system, was in place:

Connecticut gave numbers to State Highways (SH) and State Aid roads (SA). Some routes were signposted, some not. There does not appear to be a strict match to SH vs. SA and route number or signed vs. unsigned. For now, I tend to refer to both SH and SA as SH unless the distinction matters (and I have information about it).

Route numbers were probably added chronologically and as needed. This resulted in an organically grown, complicated system of short routes. By the early 1930s, the Highway Department saw the need to reorganize the system, even at the cost of a highly disruptive change.

Great Renumbering

On January 1, 1932, Connecticut renumbered nearly all its routes, in a sweeping change intended to simplify route markings and make navigation easier. Free road maps showing all the changes were distributed statewide a few weeks later.

The Great Renumbering was announced as part of a four-state agreement, including Massachusetts, Rhode Island, and New York. It should be clarified that the other four states did not renumber their entire systems as well; Massachusetts and Rhode Island had abandoned the three-digit state route system earlier, in the late 1920s. However, cross-border route changes, like those for Route 14 and Route 32, were coordinated with neighbor states.

Many of today's state routes were created then, even though most have been modified since then. A very few (such as Route 45) appear to have had no location changes at all.

Route Listing

Here's a condensed listing of what route number went where in the 1920s. After the 1920s route number (referred as "SH"), I show its approximate path using present-day route numbers ("CT", "US"). Key: [SL - state line; UC - under construction; RI - Rhode Island; MA - Massachusetts; amb. - ambiguous]

The 100s

101 CT 198 from US 6 to US 44; then US 44 E to RI SL (1923-31)
102 CT 85, Colchester to New London (1923-31)
103 CT 14, from CT 12 to RI SL (1923-31)
104 CT 17, from CT 2 to CT 66 (1923-31)
105 CT 190, from US 5 to CT 32 (1923-31); extended to MA SL along 190 and old W. Cross Hwy (1931)
106 CT 81, entire length (1923-31)
107 CT 74; from CT 83 to US 44 (1923-31)
108 New State Rd, Tolland Tpke from US 6 to CT 83; then CT 83 N to MA SL (1923-31)
109 US 44, from CT 31 to CT 198 (1923-31); UC between 30 and 74 in 1926.
110 CT 159, Hartford to CT 75; then CT 75 N to Suffield; then old CT 75 NE back to 159 (1923-29) (by 1931, Route 110 followed CT 159 for entire length).
111 CT 322/66, from CT 10 to CT 2 (1923-26); extended to US 6 in Windham (1926-31)
112 CT 17, from CT 66 to CT 77; then CT 77, entire length (1923-31)
113 CT 372, from CT 10, Plainville to CT 71, New Britain; then CT 71 and New Britain Ave. into Hartford. (1927, 31) (before 1926, also extended to CT 8).
114 CT 17, from CT 77 to New Haven (1923-31) UC south of CT 22 in 1926.
115 CT 185, all (1923-31)
116 CT 10, from CT 20 to CT 4 (19233-31)
117 CT 34, all (1923-31)
118 CT 10, from New Haven to Milldale (CT 322) (1923-31)
119 US 6 from Danbury to the New York state line (1923-26)
120 CT 63, from CT 8 to New Haven (1923-31)
121 US 44, from US 7 to NY SL (1923-31)
122 CT 25, from US 1 to US 6 (1923-31)
123 CT 4, from US 7 to CT 8, and US 202, from CT 8 to US 44 (1923-31)
124 CT 58, all (1923-31)
125 CT 67, from US 7 to US 6 (1923-31)
126 US 7, from US 1 to CT 35 (1923-29)
127 old CT 130, from US 7 to NY SL (1923-31)
128 US 202, from Danbury to CT 8 (1923-29); New Milford to CT 8 (1930-31)
129 CT 39/55, near Gaylordsville and US 7 (1923-31)
130 CT 63, from CT 4 to CT 64 (1926, 28, 31); CT 61 instead of 63 between 6, 109 (1929)
131 CT 37, Chimney Hill Rd and Briggs Hill Rd in Sherman; west from US 7 to NY SL
132 CT 43, all, and CT 63 from 63/43 junction to US 7 (1923-31)
133 CT 20, from CT 8 to CT 10 (1923-31)
134 US 7, New Milford to Canaan (1923 - c.1929); US 7 at that time went along NY 22!
135 old CT 141, Branford
136 CT 39 from US 7/CT 55 to Sherman center; then 37 south of there (1923-31)
137 CT 101, from 169 to 12 (1923-31)
138 CT 4, from CT 10 to US 44/CT 179, 179 to SR 565, to US 44 (1923-31)
139 CT 101, from CT 12 to RI SL (1926, 28, 29, 31); but appears to take older route slightly to south
140 CT 80, from CT 22 to CT 77 (1926, 29)
141 CT 14 and 14A, from US 6 to CT 12 (1923-31)
142 CT 171 from 12 to 169; CT 169 from there to MA SL (1928, 29, 31); also seen along CT 169 from 97 to 138 (1930)
143 CT 116, all (1923-31)
144 CT 205, all (1923-31)
145 along old Ousatonic Turnpike (Housatonic R, northeast bank), New Milford - Shelton
146 CT 195 and CT 89, from Willimantic to Union
147 CT 67, from CT 63 to US 6 (1923-31)
148 CT 149, all (1929, 31) [It almost got renamed to itself!]
149 old CT 15 (near I-84 path now), from CT 32 E to MA SL (1928, 29). In 1930, this became part of SH 105, and SH 149 was applied to CT 4 between US 7 and CT 41.
150 CT 156, from CT 82 to US 1 (1923-31)
151 old CT 197, from CT 32 to MA SL (1926, 28, 29, 31)
152 CT 45, all (1928, 29, 31)
153 CT 82, all (1928, 29, 31)
154 CT 47, all (1928, 29); in 1931, included Middle Rd Tpke, White Deer Rock Rd, and Charcoal Ave in Middlebury as well.
155 old CT 130, from 7 to 202 (1930)
156 CT 25, from US 6 to US 7 (1928, 29, 31)
157 US 6, from CT 10 to CT 72 (1931); used Bristol Tpke
158 old section of old CT 57 (Newtown Tpke), from CT 58 northeast to CT 302 (1929-31)
159 old CT 134 (1930)
160 CT 177, Unionville - Plainville (1926)
161 CT 302, from CT 58 to Newtown Tpke (1930)
162 old CT 72, from US 5 to New Britain, then 71 north into New Britain (1929, 31)
163 CT 4, from US 202 to Burlington town line (1931); to US 202 (1930)
164 CT 83, CT 2 to US 6 (1929-31)
165 CT 94, CT 2 to Buckland School, just E of CT 83 (1930, 31)
166 CT 30, from CT 74 to CT 190 (1928, 29, 31)
167 CT 151, from CT 66 TO CT 149 (1930)
168 CT 87, all (1928, 29, 31); also seen for CT 4, from CT 69 to Torrington (1931)
169 CT 148, small part in Chester (1930)
170 New London Tpke, from CT 2 to CT 32 (1929)
171 CT 142, all (1931)
172 CT 69, from Waterbury to US 6 (1928, 29, 31)
173 CT 110, west of 108, Shelton (1926-31)
174 CT 183, from US 44 to CT 182; poss. CT 182 to US 44 (1926, 28, 31) (in 1929, former is SA 314)
175 CT 80, most (1929-31)
176 CT 33, from US 7 to US 1 (1929, 30)
177 CT 16/old 171, from CT 66 to CT 149 (1928, 29, 31)
178 CT 71, from Meriden to New Britain (1929, 31)
179 CT 2A, from CT 12 to CT 2 (1929)
180 part of CT 107 and 58, near CT 302 in Bethel (1929, 30)
181 CT 30, CT 83 to CT 74 (1931)
182 CT 133, all (1926, 29, 31)
183 CT 198, from US 44 to CT 171; then CT 171 from there to CT 12 (i.e. old CT 91) (1931)
184 CT 123, from CT 124 to US 7 (1928, 29, 31)
185 CT 193 and 200, short loop of 12, Thompson
186 Hartford Turnpike, State St, New Haven area (1926, 31); also, _both_ the previous def. and a road near CT 58 in Bethel (1930)
187 CT 169, from CT 2 to CT 97 (1930)
188 CT 161, all (1929)
189 not yet found (a few higher odd-numbered roads were found)
190 CT 79, all (1928, 29, 31)
191 not yet found
192 not yet found
193 old CT 106, Easton
194 CT 39, from New Fairfield Center to Sawmill Center
195 CT 121, all (1930, 31)
196 CT 199, all (1930)
197 not yet found
198 two conflicting descriptions, even on same map: a) old 199 south of CT 67, 1930; b) Litchfield Tpke, from 42/63 to 69/63, Bethany
199 CT 157, from CT 66 to CT 147 (1930)

The 200s

200 CT 115 (1930)
202 CT 72, from US 6 to CT 4 (1931)
204 Old CT 179, along east side of what is now Barkhamsted Reservoir, from CT 20 to US 44 (1930, 31)
206 CT 189, 20 to MASL (1930)
208 CT 191, from 190 to 140 (1930)
210 CT 195, from US 44 to CT 89 (1930)
212 not yet found
214 CT 289, all (1930)
216 CT 49, all (1931)
218 not yet found
220 Cross Highway, from SH 180 (CT 107) to SH 158 (CT 58), Redding
222 CT 203, all (1930)
224 old 159 (Cherry Hill Rd) (1930)
226 old CT 150, from US 5 to CT 17 (1931)
299 CT 341, from US 202 to CT 45 (1930)

The 300s

300 CT 104, all (1926, 29)
301 CT 182, all (1929); CT 112 (1930). Perhaps 1929 was a typo; see SH 174.
302 CT 124, all (1926, 29)
303 Thompsonville Rd, Suffield, across river to Main St, Enfield (1926); part of old CT 190
304 CT 33, from US 7 to CT 35 (1926, 29)
305 CT 315, all (1928, 31); but also seen for CT 136 in Darien (1930)
306 CT 59, Bridgeport to Easton, then west to end at CT 58 (192x, 29)
307 CT 191/140, from US 5 to CT 83 (1928, 29, 31)
308 CT 111, from CT 25 to CT 34 (192x, 29)
309 CT 128, all (1926)
310 CT 209, 109 from US 202 to CT 61 (1929, 31)
311 old CT 184 (now parts of 178 and 187) (1929, 2x)
312 CT 272, from CT 4 to US 44 (1926, 28, 29, 31)
313 CT 30, from US 5 to CT 83, South Windsor (1929, 2x)
314 CT 183, north of US 44 (1929)
315 CT 31, south of US 44 (1926)
316 old CT 8 (better yet, old CT 65), from CT 34 to US 1 (1926, 29)
317 Silver Lane/Roberts St, from US 5 to US 6, E. Hartford/Manchester (1928, 31)
318 CT 137, all (1931)
319 New Lane, Mill St, West St, Cromwell (1930)
320 CT 177, from CT 72 to US 44 (1929)
321 CT 138, amb. (1926, 29)
322 CT 152, all (1929, 2x)
323 CT 70, west of CT 10 (1929, 31)
324 CT 122 (1930)
325 CT 68, from CT 10 to CT 8 (192x), and also CT 70, from CT 10 to Meriden (1930)
326 CT 120, all (192x)
327 CT 182 and 182A, from 44 to 183 (1931)
328 CT 187, from CT 189 to CT 190/168; then east to CT 75 (192x)
329 CT 102, all (1929-31) [does not include 1950s extended CT 102]
330 CT 147 (roughly), all (1929, 2x)
331 CT 184, from CT 12 to CT 201; then CT 201 to CT 2 (1929, 2x)
332 CT 153, all (1929, 2x)
333 CT 156, south of US 1 (1929, 31)
334 CT 32, from CT 190 to MA SL; continues as MA 32A (1929, 31)
335 older CT 136, from Norwalk to Southport; all south of US 1 (192x)
336 CT 193, all to MA SL (1926, 29, 31)
337 CT 162/122, from Milford to New Haven; ends on Beach St at Marathon Ave (1926-31)
338 CT 154, loop south of US 1 only (1929, 2x)
339 CT 73 (roughly), from Waterbury to Watertown at US 6 (192x)
340 CT 213, south from US 1 to dead end at beach (1929, 2x)
341 CT 63, from CT 8 to CT 188; then CT 188 to CT 64 (1931)
342 CT 215, east half only, with dead end at beach (192x)
343 old CT 20, Windsor Locks to East Granby (now crosses airport) (1926)
344 CT 27, all (192x)
345 CT 97, 3-cornered jog between US 44, US 44/169, Putnam (1926)
346 CT 3, from CT 372 to CT 66 (192x)
348 Lacy Rd, from CT 63 to 69; then CT 69, from CT 68 to old US 6A, Waterbury (1929-31)
350 along US 6, Watertown to Thomaston (1929, 2x)
354 CT 207, east of CT 87 (1929-31); also CT 97 from 207 to Norwich (1930)
356 CT 169, from CT 12/97 (roughly) to CT 138; then 138 east to 12 again (1929, 2x)
358 North St, Greenwich (1926, 29, 31)
360 CT 41, from 343 to NY SL (1931) (in 1929, part of US 7)
362 old CT 75, all (1931) (1929: part of CT 110)
364 CT 163, south of CT 82, Montville
366 SR 534 and CT 85, from Manchester to Colchester (1926-31)
368 CT 108, CT 8 to Stratford (1926)

Sources