It's a bit difficult to say what the "average" Roman city dweller did for work, partly because demography (people statistics) is a tricky subject when we're looking at the Romans, for whom we have so little data. What survives is a fraction of a fraction of what the Romans left behind, and they provide a reasonably skewed view of...well...people. The letters and books which remain have survived simply due to the selections of various monks and Arabian scholars who had the foresight to copy them - and those are, as might seem apparent, not particularly focused so much on the raw data as they are on the stories. There are some fun stories in there, to be sure, but, like I mentioned in the above comment, people like Seneca were part of the aristocracy and so are inherently biased. Historians are generally trained to read between these lines, but there's only so much we can do without a time machine. For example, you'll notice in the above quote that there are some professions which are mentioned offhand, in the form of a complaint: the armpit-pluckers, the masseuses (probly a slave but hey), the confectioners, the cakesellers, the sausage-makers, the food vendors, the carriage drivers, the litter-bearers, the saw sharpeners, or the aspiring musicians.

The thing is, we can't really discount the slaves in this list - they made up a substantial portion of the population, and while their jobs ranged from menial to what we would consider white collar, their contributions to the workforce were pretty incredible. Within the city, they could be assigned to almost any job imaginable - the Imperial secretaries were slaves who commanded a greater respect than many freeborn citizens. The Colosseum was built by slaves under the direction of foremen - probably also slaves - who were under the direction of architects (who we know nothing about other than the magnificent product of his/their design).

The availability of slaves in a certain profession obviously depended on how able a person in that line of work may have been able to afford slaves. While the resources of the Emperor to command enormous projects, requiring the resources of thousands of men, were essentially infinite (depending on the Emperor and how good/terrible he was at managing said cash), a baker or dyer may not have been able to afford any slaves.

Honestly, if I had to pick a "Stereotypical Roman Job" it'd be tough because there were professions for everything imaginable - but for an unskilled labourer, construction was always a fair bet. Rich people like building things, and slaves could be more expensive than free labour. Or perhaps stone-carvers. Or dyers. Or...y'know what, I'll get on to my next point.

So would a person have to go through a commute with shitty traffic? Well the decree against large carts being on the streets between certain hours certainly suggests that. Here, I'll let you read it real fast:

In the roads which are or shall be within the city of Rome, or within the limit of continuous habitation, no person, after the first day of January next following, shall be allowed in the daytime, after sunrise or before the tenth hour of the day, to lead or drive any heavy wagon; except where it shall be requisite, for the sake of building the sacred temples of the immortal gods or carrying out some public work, to draw or convey material into the city, or where, in pursuance of a contract for the demolition of buildings, it shall be requisite for public ends to carry material out of the city or away from such places, and in cases and for objects for the which it shall be lawful for specified persons and for specified causes to lead or drive such wagons.

On all days when the Vestal Virgins, the rex sacrorum, and the flamins shall be required to ride in wagons in the city for the sake of the public sacrifices of the Roman people, or when wagons shall be required for a triumphal procession on the day fixed for such triumph, or for games which shall be publicly celebrated within the city of Rome or within one mile of the city, or for the procession at the Ludi Circenses, for all such causes and on all such days it shall be lawful for wagons to be led or driven in the city in the daytime, notwithstanding any enactments in this law.

It shall be lawful for wagons, brought into the city by night, drawn by oxen or horses, if returning empty or conveying away refuse, to be in the city of Rome or within one mile of the city after sunrise in the first ten hours of the day, notwithstanding any enactments in this law.^1

Pretty cut and dry legalese here, and it outlines a couple of the issues (and exceptions that were successfully lobbied for). These are further illustrated by the literal roadblocks that the Romans used to keep wagons on pre-approved roads. The blocks were essentially curbs, which would be nigh impossible for a wagon, already in the existing ruts, to cross. So, if you were a hypothetical merchant or farmer (not quite a resident of Rome, but bear with me), you'd show up to the city in the pre-dawn hours to deliver your wares. But wait! First, you've gotta make it through the gates. The gates of Rome (and other Roman cities, but we're talking about Rome here) were an enormous bottleneck. With a few exceptions, wagons paid tolls on their goods before making their way into the city. If you've ever been to a customs checkpoint, you get the idea. Now imagine that the customs checkpoint only has one lane, and it's the only way into New York City. Congestion around the gates was endemic, since city gates were built with defence in mind - and thus were often relatively narrow. A good number of cities only had a one lane gate, with a smaller, secondary, one for pedestrians. Then, on top of all of this, Rome was not built as well as the coloniae or cities like Alexandria, which were founded on a grid. Rome's streets were....a glorious mess, to put it very kindly. Livy describes/blames it thus:

The proposed measure for migration was dropped, and they began to rebuild the City in a haphazard way. Tiling was provided at the public expense; every one was given the right to cut stone and timber where he pleased, after giving security that the building should be completed within the year. In their haste, they took no trouble to plan out straight streets; as all distinctions of ownership in the soil were lost, they built on any ground that happened to be vacant. That is the reason why the old sewers, which originally were carried under public ground, now run everywhere under private houses, and why the conformation of the City resembles one casually built upon by settlers rather than one regularly planned out.^2

The problems here were exacerbated by the terrain, since the city was built on a bunch of hills next to a twisting river. So, of course, everything was built around those, which...doesn't help. The population density was also enormous, with most scholars estimating that there were at least a million people in Rome in the Early Empire, which suggests an extraordinary level of population density, especially since the city was not particularly large, geographically. Here are a few quotes for you on the traffic problems, laws nonwithstanding:

In hot haste rushes a contractor with mules and porters; a huge crane is hoisting now a stone and now a beam; mournful funerals jostle massive wagons; this way runs a mad dog: that way rushes a mud-bespattered sow. ... Would you wish me, amid noises by night and noises by day, to sing and pursue the minstrels’ narrow pathway?^3

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The crossing of wagons in the narrow winding streets, the slanging of drovers when brought to a stand, would make sleep impossible for a Drusus – or a sea-calf. When the rich man has a call of social duty, the mob makes way for him as he is borne swiftly over their heads in a huge Liburnian car. He writes or reads or sleeps inside as he goes along, for the closed window of the litter induces slumber. Yet he will arrive before us; hurry as we may, we are blocked by a surging crowd in front, and by a dense mass of people pressing in on us from behind: one man digs an elbow into me, another a hard sedan-pole; one bangs a beam, another a wine-cask, against my head. My legs are beplastered with mud; soon huge feet trample on me from every side, and a soldier plants his hobnails firmly on my toe. See now the smoke rising from that crowd which hurries as if to a dole: there are a hundred guests, each followed by a kitchener of his own. Corbulo himself could scarce bear the weight of all the big vessels and other gear which that poor little slave is carrying with head erect, fanning the flame as he runs along. Newly-patched tunics are torn in two; up comes a huge firlog swaying on a wagon, and then a second dray carrying a whole pine-tree; they tower aloft and threaten the people. For if that axle with its load of Ligurian marble breaks down, and pours an overturned mountain on to the crowd, what is left of their bodies? Who can identify the limbs, who the bones? The poor man’s crushed corpse wholly disappears, just like his soul.^4

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Consider this city, in which the throng that streams ceaselessly through its widest streets is crushed to pieces whenever anything gets in the way to check its course as it streams like a rushing torrent, – this city in which the seating space of three theatres is required at one time.^5